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Prepare a roof washer system (also named first or foul flush device) to avoid that the first rains rinsing the roof would enter into the water reservoir. Several foul flush devices exist, like factory made models based on the principle of a vortex which keeps the dirt particles in suspension, while only clean water can pass into the reservoir. It is also possible to make some simple systems locally, like:


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➞ a vertical pipe with a diameter of at least 4” descending at every 10 m of gutter length, closed at the bottom


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with a watertight but removable cover (as per figure B). The first (dirty) rainwater will be collected in the descending pipe until it is full, and then clean rainwater will overflow into the reservoir. A small hole (2 mm diameter) should be made about 0.2 m above the removable cover, and another two on top of each other with a distance of 0.1 m (as per figure B). These holes will allow the descending pipe to drain completely once the rainfall stops. In this way, this simple but automatic device will be ready again for the next rainfall.


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➞ a grease trap alike design (T.B. 4.04, model A with elbow and T-piece) placed on top of the water reservoir, in which the dirt particles will settle. A screen (e.g. metallic mosquito netting) can be added in the middle


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of the device to stop leaves from getting into the water reservoir. Some small drain holes should be foreseen again to empty this roof washer automatically.


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Install the gutters at the edge of the roof, with a 0.2 to 1% slope towards the roof washers and down-pipes. The gutters can be factory made (e.g. PVC, metal) or locally made of a cut-in-half PVC pipe or a galvanised metal sheet folded in a rectangular section. The gutters must be solidly fixed in order to withstand a sudden and violent water influx, like is frequently occurring in tropical areas. In order not to loose too much rainwater during heavy rainfall, it is recommended to install deflectors at the edge of the roof (as per figure D).


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Foresee also additional leaves separators. These can be cones with holes that are installed in the gutter, one over each inlet of the descending and down-pipes.


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Rainwater can also be an interesting (additional) source for (acute) emergencies. Following are two ways of installing a simple emergency rainwater harvesting system:


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➞ Suspend a piece of plastic sheeting in a large U-shape to form some kind of a big gutter, which is hanging


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with its lower side inside an open reservoir (T.B. 2.35; 2.38). The upper corners of the plastic sheeting are potentially connected to an existing roof. If the roof is of poor quality or in case of a tent, new plastic sheeting can be used to cover it.


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➞ Install on a gentle slope several complete rolls of plastic sheeting overlapping each other (e.g. 5 rolls = 60 m x 16 m catchment area), with a big gutter at the lower end. A surface pump can transfer the rainwater


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For these temporary solutions, it won’t be possible to install an automatic roof washer. Thus the first rains will have to be discarded by draining the dirty water away.


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Disinfect the water reservoir and other cisterns of the rainwater harvesting system before they are commissioned and after they have been cleaned. This can be done in the same way as described for wells (T.B. 2.03, technique A). Every 2 – 3 years, they should also be examined for sludge accumulation.


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Fill the reservoir with potable water from another safe source after cleaning and disinfection works have taken place. Otherwise, it will take too long before the reservoir is filled up again with rainwater, certainly during the dry season.


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Clean the roof washers frequently to avoid accumulation of materials like leaves or sand that will block the drain holes. The gutters and the leaves separators must be cleaned regularly too.


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In urban and/or industrialized areas, it is strongly recommended not to use rainwater for drinking, feeding (cooking, washing dishes) and personal hygiene activities because the atmospheric pollution has an important impact on the water quality. In these contexts, it should thus be avoided to implement rainwater harvesting systems, unless the water will only be used for other purposes (e.g. flushing of toilets, laundry).


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The amount of rainwater that can be harvested is relatively limited. If partial and full systems are required, substantial investments will be needed for the roof and the storage reservoir. In order to reduce the needed storage capacity, the rainwater should be harvested on all the available roofs. Under certain circumstances, it will be cheaper to construct an additional roof (which in a health centre could be used as a waiting area for the patients for instance) than to build a big reservoir.


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The slope of the roof itself and its actual number of square metres are not important to determine the roof surface. It is only the ground surface covered by the roof that should be determined.


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Painted or corroded iron sheets and thatch should be avoided for rainwater harvesting. Good quality galvanized iron or plastic sheets and tiles are the preferred choice for rainwater collection. Existing asbestos-cement roofs in good condition could be considered as well. The asbestos-cement micro-fibres don’t represent any health risk when swallowed. However, they are very dangerous when inhaled. Thus the risk would be a lot higher to remove the existing asbestos-cement roof to be replaced by another material than using it directly for rainwater collection. Serious attention should still be given not to cut, break or drill in the existing asbestos-cement sheets during the installation of the gutters.


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In case rainwater is the only source of water, the reservoir size should be calculated correctly, based on the monthly rainfall data. Extreme over-sizing is too expensive and under-sizing will lead to a water shortage at the end of the dry season.


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The storage reservoir must imperatively be closed to protect the harvested rainwater from any external contamination. A manhole with a well closing lid is essential however to permit regular maintenance. The overflow of the reservoir should always be equipped with a screen to avoid that vectors would breed inside.


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Roof washers are essential, certainly if the harvested rainwater will be used as drinking water without treatment (although chlorination is always recommended for health structures). Their capacity must be sufficient for the roof to be cleaned and for the harvested rainwater not to contain impurities anymore. Their capacity should be calculated according to the surface of the roof and the environmental conditions;


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e.g. intensity and frequency of the rainfall, surrounding vegetation. A rule of thumb for correct rinsing is to foresee about 1 l/m2 of roof surface, although this will not be possible for areas with limited rainfall. At least 5 l of the first rains need to be discarded for roofs of small houses, whereas at least the first 25 l can’t be used for medium sized buildings (e.g. health centres with a roof surface of 150 m²).


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The drain holes of a roof washer have to be small not to interfere too much with the system filling up, even during light rainfall. However, due to their small size, they might get clogged rapidly which will hamper the automatic drainage of the roof washer. Therefore is a very frequent cleaning of the device of utmost importance.


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In areas where avian flue is present or suspected, it is strongly recommended to chlorinate the rainwater to a free residual concentration of at least 0.5 mg/l, after a minimum contact time of 30 minutes with the water at a pH < 8.


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The pathogenic organisms which may be present in water are too numerous and too various to be identified individually in practice. As their presence is mostly linked to faecal contamination (except for e.g. Guinea worm), it is preferable to look for organisms that are “indicators” of this pollution. These indicators should be universally present in large numbers within the faeces of humans and other warm blooded animals, should be readily detectable with relatively simple methods and should not grow in natural waters.


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The indicator organism of choice for (recent) faecal pollution is the Escherichia coliform (E. coli). Thermo-Tolerant Coliforms (TTC) can also be used as an alternative in many circumstances and certainly under field conditions, because a very high percentage (more than 80 %) of the TTC’s are E. coli anyway. The kind of indicator that will develop during a bacteriological analysis depends mainly on the culture media and the incubation temperature.


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Water for human consumption should not contain indicator organisms. The presence of Escherichia or Thermo-Tolerant Coliforms in water indicates the probable presence of pathogenic organisms, where their absence indicates the possible absence of pathogens, but is no proof of this. Certain pathogens like protozoa and some enteroviruses are more resistant than faecal coliforms to unfavourable environmental conditions and disinfectants like chlorine.


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The count of Escherichia or Thermo-Tolerant Coliforms per 100 ml gives an indication of the degree of faecal pollution. Where the ideal is set at 0 E. coli/100 ml of water, a count of up to 10 E. coli/100ml may be admissible without treating the water. Counts above this level require at least a disinfection (e.g. chlorination) that will have to be preceded by other forms of treatment when the turbidity is high (T.B. 2.12). Following table gives an appreciation of the health risk related to the amount of coliforms that are present in a 100 ml water sample.


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Bacteriological analysis are mostly performed by means of the membrane filtration method or the Most Probable Number (MPN) method. Both methods have their advantages and inconveniences. The membrane filtration method gives direct and more precise results (on non-turbid water) when performed by experienced people, where the MPN method is less but sufficiently accurate and a lot easier to perform and to interpret. Both methods can be implemented as well under laboratory as under field conditions.


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When water is (mass) distributed via taps, it should normally be treated, at least with chlorine. In these cases, the indicators (e.g. E-coli) will be eliminated by the disinfectant and the count of coliforms is less relevant. Where disinfection isn’t possible, a bacteriological analysis is strongly recommended, even in some acute emergencies (e.g. a hand pump installed on a well that has been flooded). A positive count of coliforms in the water indicates the presence of (faecal) pollution. For chronic emergencies and certainly for stabilised situations, the source of the pollution should be found and prevented first, rather than starting to treat the water. For accidental events, the pollution should be retrieved if possible and preventative measures installed.


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The chemical analysis method differs for each element that needs to be examined. As each element requires specific tests, refer to more specific literature. These tests and their interpretations are to be carried out by properly trained personnel. Based on experience, appropriate analysis must be carried out, preferably by the national authorities:


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Two main physical water characteristics are to be measured, certainly when chemical treatment like coagulation / flocculation (T.B. 2.15) and/or chlorination (T.B. 2.21) is required:


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indicates the amount of suspensible particles present in the water. Turbidity is commonly expressed in (Nephelometric) Turbidity Units or (N)TU. It is considered that a turbidity under 5 NTU permits the “most effective disinfection possible” with chlorine, at least under field conditions (T.B. 2.21). A turbidity up to 20 NTU is still acceptable to chlorinate drinking water during the acute phase of an emergency. The turbidity might also be an important factor for the acceptability by the consumers. T.B. 2.13 presents the detailed procedure to measure turbidity.


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is a logarithmic scale of the hydrogen ion (H+) concentration and indicates in practice if the water is acid (<7), neutral (=7) or basic (>7). Although the pH has no direct (health) impact on the consumers, it is one of the most important operational water quality parameters as it has an influence on some chemical water treatment procedures and on the corrosion / incrustation of the equipment (e.g. pumps, pipes). T.B. 2.22 presents the detailed procedure to measure the pH with a pool tester.


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Bacteriological and/or chemical analyses are not always necessary. It is generally much more important and useful to do a sanitary survey concerning amongst others; the origin of the water, the protection of the water point, its location in relation to defecation areas, cemeteries and waste zones, the protection of the water during transport and storage. Such a survey will often make it possible to determine if the water is polluted, or has strong chances of getting polluted at one time or another. Analyses only give an indication of pollution at the precise moment of sampling, and not of the potential risk of pollution. However, it can be relevant to do a bacteriological analysis of a well protected water source: e.g. in case there is a sudden increase of faecal-oral diseases.


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The health risk due to toxic chemicals in drinking water differs from that caused by microbiological contaminants. There are few chemical contaminants of water that can lead to acute health problems, except through massive (accidental) contamination of the supply. Most chemical contaminants of drinking water cause adverse health effects after prolonged periods (years) of exposure.


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In case water treatment is performed with chemicals, field test kits (for iron / aluminium or chlorine residual measurements) should be available to do a regular follow up of the treated water.


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Laboratories that can perform bacteriological and chemical analysis can often be found in the capital of low-income countries, and also in water treatment plants or in breweries. The main problem, in particular for bacteriological analysis, is to get the water sample on time in the laboratory. Samples should reach the analytical laboratory within the hour of sampling if they are kept at ambient temperature, or within 6 hours if they are kept at a temperature between 4 and 6 ˚C (but not frozen).


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Always work with clean hands (washed with water and soap) when performing sampling (T.B. 2.11) and water analysis. Any contamination by dirty hands can / will distort the results.


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When a new water source is put into service and if the infrastructures are available, the water sampling and analysis should be undertaken by the appropriate (national) authorities, according to the national standards. In this way, the local government will be involved in the process and the responsibility transferred to them. In acute emergencies however, this procedure might be more complicated.


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Remove the protection (seal) from the sterile bottle and take off its cap. Don’t put the cap down where its inside could get contaminated.


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Replace the cap and the protection (seal) without touching the inside of the bottle / cap, nor the water.


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Turn the bottle upright when it is at about 0.2 m under the water surface. This should be done in such a manner that the inlet is facing the current (water flow direction), in order to avoid that the water sample gets contaminated by your hand.


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Lower the bottle in the well until it is about 0.2 m under the water surface. The weighting ballast will help the bottle to sink.


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The sampling techniques for chemical analysis are similar to those for bacteriological analysis. However, even if it is still necessary to let the tap run for about 30 seconds, there is no need to respect the measures for sterile sampling (e.g. sterile bottles, flaming of the tap). A water sample for chemical analysis requires at least 2 glass or plastic bottles of 1 to 1.5 l (e.g. mineral water bottles), which must be clean and airtight.


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➞ Attach a rinsed weighting ballast and string to the closed bottle if the sample needs to be taken from a well.


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➞ Rinse the cap and the bottle 3 times with the water to be analysed, according to the sampling techniques described for bacteriological analysis.


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Fill the bottles right to the top according to the sampling techniques described for bacteriological analysis and put their cap back on (remove the weighting ballast and string from the closed bottle if necessary).


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Always work with clean hands (washed with water and soap) during sampling and water analysis. Any contamination by dirty hands will distort the results.


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The described measures for sterile sampling are not necessary for chemical analysis, but are absolutely essential for bacteriological analysis.


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Sterile 100 ml sample bottles can potentially be obtained from a laboratory or from the sterilisation department of a hospital. An alternative is to purchase sterile bottles or sterile single use sachets. If these solutions aren’t possible, it is still possible to sterilise the bottles yourself according to the following steps:


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➞ Foresee at least 2 x 100 ml bottles per sample. Glass and polypropylene (PP) bottles can be sterilised,


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but polyethylene (PE) and PVC bottles won’t resist the temperatures that will be reached in the autoclave.


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➞ Pack the bottles and caps together in a double layer of crêpe paper (don’t put the caps back on the bottles, to allow the steam to enter).


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➞ Put the package upside-down in the autoclave, in such a manner that the opening of the bottles are pointing downwards.


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➞ Sterilise the package at 1.05 bar (121 °C) for 20 minutes according the instructions of the autoclave’s manufacturer. This should preferably be done by an experienced person (e.g. in a health centre).


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➞ Keep the crêpe paper package at a safe place until the sterile bottles are used, which should be within the 2 weeks following the sterilisation (if not, the procedure should be repeated).


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➞ Take them out of the water after 20 minutes of boiling, and let them cool, whilst protecting the opening with flamed aluminium foil or a sterile compress.


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Never touch the inside of the sterilized bottle / cap. When sampling, hold the cap by the outside; never put it down unless it is upside down. It is better, for security and reliability, to double each sample.


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The weighing ballast should be disinfected before the water sample is taken: remove all the potential dirt, boil it for 20 minutes or flame it with alcohol.


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For a bacteriological analysis of water that has been chlorinated, a sodium thiosulphate solution has to be added to each sampling bottle before sterilizing. This product will neutralize the chlorine of the water sample, which would otherwise affect the results. Single use sterile sachets with integrated sodium thiosulphate are also existing. Contact your technical referent for more information.


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➞ an identification number, the sampling place and the water source type (as accurately as possible);


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Laboratories that can perform bacteriological and chemical analysis can often be found in the capital of low-income countries, and also in water treatment plants or in breweries. The main problem, in particular for bacteriological analysis, is to get the water sample on time in the laboratory. Samples should reach the analytical laboratory within the hour of sampling if they are kept at ambient temperature, or within 6 hours if they are kept at a temperature between 4 and 6 ˚C (but never frozen).


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In case it isn’t possible to get the water samples on time in the laboratory, the only alternative to perform a bacteriological analysis is with field testing kits (e.g. membrane filtration or the Most Probable Number methodology; see the respective user’s manuals).


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In case water treatment is performed with chemicals, field test kits are essential to do a regular follow up of the treated water (iron / aluminium and/or chlorine residual measurements).


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The main objective of water treatment in precarious situations is the elimination of pathogens. The treatment methods to obtain this objective are:


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Heating can destroy the pathogens. Boiling water is an effective way to disinfect small quantities of water (even when turbid) if it is performed correctly, but it doesn’t protect against any further contamination (no remnant effect). To be completely sure that all pathogenic organisms are destroyed, the water should be brought to a rolling boil for at least one minute (although there is a lot of discussion on the minimum time needed), augmented by one minute for each altitude increase of 1000 m. This treatment method consumes a lot of energy and influences the taste of the water (which can be remedied by re-oxidizing the water by means of stirring or pouring it into another clean recipient).


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UV light has the capacity of eliminating most pathogens, but it does not give a remnant protective effect to the treated water. However, UV irradiation can be a very interesting treatment method against pathogens which aren’t affected by chlorine at normal drinking water concentrations; e.g. Hepatitis E virus. Another interest for UV irradiation (on big scale treatment) is when adding chlorine gives a significant colour variation of the treated water.


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Special UV- C lamps have been developed to disinfect big quantities of non-turbid water in very short times, but they are rather fragile. After their foreseen lifespan (information provided by the manufacturer), they should be replaced, even when they still seem to function. The reason is that their irradiation frequency has shifted too far away from the ideal bactericidal wavelength (254 nm).


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For small quantities of non-turbid water (< 20 - 30 NTU; T.B. 2.13), the principle of UV irradiation can also be achieved by the sun. Water stored in smooth, scratch free and transparent plastic (PET) 1 - 1.5 l bottles will be disinfected, but it requires long periods of full sunlight to be effective. This can be improved by painting one side of the bottle black or by placing it on a black corrugated iron sheet in order to increase the temperature of the water as well. The exposure time to full sunlight still needs to be 6 - 8 hours.


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Certain filtration procedures are able to eliminate pathogens from raw water. Surface filters will remove all particles, including the pathogens that are bigger than their pore size, whereas smaller particles will remain in the water. These filters include ceramic candle and membrane filters. To avoid clogging, a frequent cleaning or replacement of the filters will be required. Slow sand filtration on the other hand uses a mechanical filtration combined with a natural biological membrane of micro-organisms that feed on organic matter, including pathogens. They are capable of removing suspensible particles as well, but if the turbidity is higher than 30 NTU, rapid clogging of the filters will occur (T.B. 2.17). A pre-treatment like roughing filters is thus required in order to have a cleaning frequency of once every two months. None of the filters give a remnant protective effect.


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Several chemicals such as chlorine, ozone and iodine can disinfect water. All products have their advantages and inconveniences, but most of the aid-agencies will disinfect water with chlorine (T.B. 2.19 to 2.23). The disinfection procedure with chlorine is rather easy to perform, relatively cheap and efficient against most bacteria and viruses. Another big advantage of chlorine is that it gives a remnant protective effect. It means that if a correct chlorine concentration has been added, a small accidental contamination of the treated water will be eliminated. However, at the concentrations used for drinking water, chlorine will not harm the protozoan cysts (Giardia or Cryptosporidium) nor the helminth eggs, which cause still a health hazard.


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Chlorine won’t be effective either if the water is turbid. Therefore is it important to measure the turbidity and if needed to remove it before the water is chlorinated. Disinfecting drinking water with chlorine, alone or in combination with pre-treatments, should systematically be done, certainly in emergencies and health structures.


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Because of the existence of huge amounts of different chemical substances, it is difficult to determine if the water is polluted and even more so by what substance (although a lot of different chemical analysis kits are existing; for more information, contact your technical referent). Additionally, the removal of chemicals is often difficult and expensive. Most of the water treatment methods available on the field are only capable of removing few chemical substances, but which can have their influence on taste, odour and colour. Hence, it is recommended to change water sources as soon as possible if there is a suspicion of chemical pollution.


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Turbidity is a measure indicating the amount of suspensible particles in the water (T.B. 2.13). As such, it will directly affect the acceptance of the water by the consumers. Most disinfection methodologies are only really effective when no or a little amount of particles are present in the water. When measured (with a turbidity tube), the value should be less than 5 (N)TU, and certainly less than 20 (N)TU (for acute emergencies). If the turbidity exceeds these recommended values, a pre-treatment such as sedimentation (natural or assisted) and/or filtration should be done before disinfection can be initiated.


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Natural sedimentation is a process where the raw water is stored in a recipient over a certain period for the particles in suspension to fall down by gravity. The longer the period, the more particles will settle at the bottom of the water recipient, although this can take a very long time. These falling particles will also trap some pathogens and carry them to the bottom of the recipient where they will die over time. The long waiting times (several hours up to several weeks) make that this procedure is not very practical, and even unfeasible for emergencies. Water stored for longer periods also has to be protected from the sun to avoid algae growth, from breeding mosquitoes, from dust and other contaminants entering the recipient.


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To speed up the sedimentation process, biological or chemical products (e.g. aluminium sulphate, ferric chloride) can be added to the water (T.B. 2.14 to 2.16). These products, the so-called coagulants, help the very small particles in suspension to aggregate into bigger and heavier flocks (higher density), so that they fall faster to the bottom of the recipient. As the process is assisted by adding coagulants, it is called assisted sedimentation.


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Assisted sedimentation reduces the turbidity drastically, but to get under 5 NTU (the appropriate value for an effective chlorination) requires a waiting time that is often still too long for emergencies. The addition of flocculants or the use of polymers can reduce the sedimentation time (T.B. 2.14).


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The residual concentration of chemical coagulants after assisted sedimentation without filtration are often too high according to the WHO directives. These residuals may have a negative impact on public health or on the acceptability of the drinking water by the beneficiaries. Assisted sedimentation does not completely remove pathogens like protozoan cysts and helminth eggs either. For all these reasons, water should preferably also be filtered before disinfection, certainly if a very low turbidity is required (e.g. for health structures).


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Filtration processes (T.B. 2.17) use a porous environment to separate the solids from the water. The porous environment lets the liquid pass while the solids are stopped. As described above, the surface filters and slow sand filters can reduce the turbidity, but they will clog (rather) rapidly. As the clogging isn’t such a big problem for rapid sand filters, they are often considered as the preferred choice for filtration in emergencies. This filtration method can either be the next step following assisted sedimentation, or it can be direct but assisted with a coagulant (coagulated / flocculated water directly filtered on the sand) and then followed by chlorination.


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RemarksSources that are completely protected (e.g. protected wells or boreholes equipped with a good hand pump) and providing safe water can be exempted from treatment. However, when these sources are equipped with a motorised pump and a centralised storage system (e.g. health centres), it is recommended to chlorinate their water anyway to obtain the remnant effect.Only non-turbid raw water can be considered for simple chlorination, although that protozoan cysts and helminth eggs often survive this disinfection method and still cause health hazards. Thus different treatment methods will have to be combined in certain situations, certainly when the raw water is turbid. Some different scenarios as examples:➞ Acute emergency: turbidity < 20 NTU => simple chlorination (still risk of cysts / eggs).➞ Acute and chronic emergency: turbidity > 20 NTU:- assisted sedimentation + chlorination (still risk of cysts / helminth eggs).- assisted direct rapid sand filtration + chlorination (good quality


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Acute and chronic emergency: turbidity > 20 NTU:- assisted sedimentation + chlorination (still risk of cysts / helminth eggs).- assisted direct rapid sand filtration + chlorination (good quality water, limited to 300 NTU).- assisted sedimentation + rapid sand filtration + chlorination (good quality water).➞ Stabilized situation: preferably water sources not needing any treatment (except chlorination).


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<table><tr><td/><td>Natural sedimentation</td><td>Assisted sedimentation</td><td>Ceramic candles</td><td>Membrane ultra / nano filtration</td><td>Slow sand filtration</td><td>Rapid sand filtration (assisted with coagulant)</td><td>Chlorination (with normal concentrations used for potable water)</td></tr><tr><td>Turbidity</td><td>1 (long waiting time)</td><td>3 (rather long waiting time to reach very low turbidity)</td><td>3 (rapid clogging, frequent cleaning)</td><td>3 (rapid clogging, frequent backwashing)</td><td>2 (max 30 NTU, need for roughing filters)</td><td>3 (up to 300 NTU)</td><td>0</td></tr><tr><td>Bacteria (+/-0.1-20 µm*)</td><td>1 (long waiting time)</td><td>1</td><td>3</td><td>3</td><td>2 to 3</td><td>0 (1 if assisted with a coagulant)</td><td>3</td></tr><tr><td>Viruses (+/-0.01-0.25 µm)</td><td>0 to 1 (long waiting time)</td><td>1</td><td>2</td><td>3</td><td>1 to 2</td><td>0 (1 if assisted with a coagulant)</td><td>2 (some viruses will survive)</td></tr><tr><td>Protozoa &amp; Helminth eggs (+/-1-100 µm)</td><td>0 to 1 (long waiting time)</td><td>1</td><td>3</td><td>3</td><td>3</td><td>3</td><td>1</td></tr><tr><td>Salt</td><td>0</td><td>0</td><td>0</td><td>1</td><td>0</td><td>0</td><td>0</td></tr><tr><td>Colour, odour and taste</td><td>1</td><td>1</td><td>1</td><td>2</td><td>2</td><td>2</td><td>1</td></tr><tr><td>Remarks</td><td>- not often used due to its low efficiency</td><td>- turbidity reduction in emergency. -post rapid sand filtration desirable -post- chlorination compulsory</td><td>-small production -staff houses -small health structures -domestic treatment</td><td>-rather fragile -expensive -post- chlorination recommended</td><td>-slow production -small health structures post- chlorination recommended</td><td>-camps -health structures -post- chlorination compulsory</td><td>-camps always -recommended in health structures -domestic treatment -remnant effect</td></tr></table>


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Natural sedimentation Assisted sedimentation Ceramic candles Membrane ultra / nano filtration Slow sand filtration Rapid sand filtration (assisted with coagulant) Chlorination (with normal concentrations used for potable water) Turbidity 1 (long waiting time) 3 (rather long waiting time to reach very low turbidity) 3 (rapid clogging, frequent cleaning) 3 (rapid clogging, frequent backwashing) 2 (max 30 NTU, need for roughing filters) 3 (up to 300 NTU) 0 Bacteria (+/-0.1-20 µm*) 1 (long waiting time) 1 3 3 2 to 3 0 (1 if assisted with a coagulant) 3 Viruses (+/-0.01-0.25 µm) 0 to 1 (long waiting time) 1 2 3 1 to 2 0 (1 if assisted with a coagulant) 2 (some viruses will survive) Protozoa & Helminth eggs (+/-1-100 µm) 0 to 1 (long waiting time) 1 3 3 3 3 1 Salt 0 0 0 1 0 0 0 Colour, odour and taste 1 1 1 2 2 2 1 Remarks - not often used due to its low efficiency - turbidity reduction in emergency. -post rapid sand filtration desirable -post- chlorination compulsory -small production


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and taste 1 1 1 2 2 2 1 Remarks - not often used due to its low efficiency - turbidity reduction in emergency. -post rapid sand filtration desirable -post- chlorination compulsory -small production -staff houses -small health structures -domestic treatment -rather fragile -expensive -post- chlorination recommended -slow production -small health structures post- chlorination recommended -camps -health structures -post- chlorination compulsory -camps always -recommended in health structures -domestic treatment -remnant effect


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In grey: the treatment procedures most commonly used by aid-agencies, often in combination with other methods 0: no impact, 1: low impact, 2: medium impact, 3: high impact - * µm = micron = 10-6 m


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The simplest and cheapest method to measure the turbidity is to use a turbidity tube, but it is unfortunately also a subjective measurement. A turbidity tube is often available in aid-agencies’ chlorination kits and in some bacteriological analysis kits. The turbidity tube is a long and narrow graduated tube, in transparent plastic with a black ring or cross printed on the bottom. The measurements with a turbidity tube are expressed in (Jackson) Turbidity Units, or (J)TU.


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To measure the turbidity in a more objective manner, electronic instruments are required. Several electronic measurement principles are existing, each with their own precision and price tag. The most precise electronic turbidity meters measure under 90° the remaining intensity of the light that has been emitted by a specific lamp through a water sample, potentially compared to a light intensity measurement at 180°. With this principle, the measured values are expressed in Nephelometric Turbidity Units (NTU), which is also the most commonly used unit.


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Because extreme high precision is mostly not needed on the field and due to the prize, most turbidity measurements will be done with the tube. Note that some turbidity tubes have wrongfully a NTU scale, but as it’s a similar scale to JTU, it doesn’t really matter. Anyway, other turbidity units than JTU and NTU exist (depending on the electronic measurement system), all with a similar scale.


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Try to detect via the opening and through the mass of water the black ring or cross at the bottom of the tube. This has to be done with the tube in vertical position.


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Remove gradually water from the tube (if necessary) until the black mark on the bottom can be detected.


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Read the result by comparing the water level in the tube and the graduation present on the tube wall. This has to be done with the tube in vertical position.


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Coagulants have the potential to neutralise the electrical repulsion phenomena that keep the particles in suspension within the raw water. Once the right amount of coagulant (often under the form of a solution) has been added and well mixed with the water to be treated, the neutralised particles can join each other and start to grow into flocks (flocculation). Some additional products, so-called flocculants (sometimes a combined product) can be added to speed up the flocculation process. In order to determine the right dose of the coagulant / (flocculants) to be added, a jar test has to be performed on the raw water (T.B. 2.15).


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As these flocks have become bigger and heavier (higher density) than the original particles (due to the coagulation / flocculation processes), they will start to settle down within the water recipient / reservoir. This will improve the turbidity of the treated water drastically (T.B. 2.16).


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It is also possible to retain the formed flocks directly from the water by means of a rapid sand filter, without having to pass the sedimentation process (T.B. 2.17). Direct Rapid Sand Filtration will improve the quality of the treated water even more in comparison with assisted sedimentation, but is limited for very high turbidities (the filtration periods become very short if the turbidity of the raw water exceeds 300 NTU).


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A combination of assisted sedimentation with rapid sand filtration is possible as well when water with an extremely high turbidity needs to be treated and high quality water is required.


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Aluminium sulphate, Al2(SO4)3 is the best-known coagulant worldwide and it can be found in most (low-income) countries (e.g. often stored in water treatment plants).


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Polymers are very effective coagulants / (flocculants). These products become available as well under


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Some biological products such as grinded Moringa oleifera tree seeds exist as well. They are not commonly used for big scale treatment, but rather at domestic level.


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The following table gives a comparison of different chemical coagulants, often used by aid-agencies:


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<table><tr><td>Product</td><td>Advantages</td><td>Disadvantages</td></tr><tr><td>Aluminium</td><td>crystallised (sometimes lumps)</td><td>available only at low</td></tr><tr><td>sulphate</td><td>often available on the field not expensive no expiry date often known by national counterparts</td><td>concentration (w/w*: 17 - 18%) mainly usable within a pH-range of 6.0 to 7.4 (T.B. 2.10) rather difficult to dissolve</td></tr><tr><td>Ferric chloride</td><td>crystallised (but also available as a liquid) high concentration (w/w.*: 60%) usable in a wide pH-range of 5.0 to 9.0 (T.B. 2.10) not expensive at purchase no expiry date (stable, even dissolved) easy to dissolve no (IATA) air transport regulation</td><td>rarely available on the field importation needed water might turn yellowish corrosive granules absorb very quickly humidity, becoming a wet paste or a solid block when dried out again (resulting in difficulties to prepare a mother solution)</td></tr><tr><td>Polymers</td><td>extremely good coagulants / flocculants usable in a very wide pH-range of 4.0 to 9.0 (T.B. 2.10) normally little amounts needed</td><td>often low concentration available dosage can be difficult rarely available on the field importation needed not stable during long period possible (IATA) air transport regulation</td></tr><tr><td/><td>* w/w: weight for weight</td><td>possibly expensive</td></tr></table>


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Product Advantages Disadvantages Aluminium crystallised (sometimes lumps) available only at low sulphate often available on the field not expensive no expiry date often known by national counterparts concentration (w/w*: 17 - 18%) mainly usable within a pH-range of 6.0 to 7.4 (T.B. 2.10) rather difficult to dissolve Ferric chloride crystallised (but also available as a liquid) high concentration (w/w.*: 60%) usable in a wide pH-range of 5.0 to 9.0 (T.B. 2.10) not expensive at purchase no expiry date (stable, even dissolved) easy to dissolve no (IATA) air transport regulation rarely available on the field importation needed water might turn yellowish corrosive granules absorb very quickly humidity, becoming a wet paste or a solid block when dried out again (resulting in difficulties to prepare a mother solution) Polymers extremely good coagulants / flocculants usable in a very wide pH-range of 4.0 to 9.0 (T.B. 2.10) normally little amounts needed often low concentration available dosage


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a mother solution) Polymers extremely good coagulants / flocculants usable in a very wide pH-range of 4.0 to 9.0 (T.B. 2.10) normally little amounts needed often low concentration available dosage can be difficult rarely available on the field importation needed not stable during long period possible (IATA) air transport regulation * w/w: weight for weight possibly expensive


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Polymers are often used under their pure form because their coagulation / flocculation procedure starts already with the elements of the water that is used to make the mother solution.


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Ferric chloride and aluminium sulphate must be used under a liquid form, mostly a 1% mother solution, although other concentrations might sometimes be required as well. The preparation is similar as for chlorine solutions (T.B. 2.20):


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With	X = grams of product to be added per litre of water to reach the desired solution concentration (g/l) Y = desired solution concentration (%)


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N = 10 g/l: equal to the amount of coagulant needed to make 1 litre of 1% mother solution if its concentration would be 100%


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(calculation: 1 l of water weighs 1000 g ; 1% of 1000 g = 10 g and 1% solution = 10 g/l) C = concentration of the coagulant’s concentration (w/w); as mentioned on the packaging (%)


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Based on effectiveness, polymers are by far the best coagulant / (flocculants) for assisted sedimentation. These products are mostly so effective that only very little amounts of them need to be used. They are effective in a wide pH variety of the raw water, and they form big flocks that can settle down rapidly. Due to the formation of big flocks, these products are less suited for direct rapid sand filtration because they might clog up the filtration medium.


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As it is often difficult to make a mother solution with polymers, they have to be mixed directly with the raw water under their pure form. This can render the fine tuning of the assisted sedimentation process quite difficult and a jar test nearly impossible. An insulin syringe (1 ml) could be used to attempt a jar test with 1 litre beakers, as only a few drops of pure liquid polymer are needed. As such, the jar test will stay an approximation, but still precise enough to start the emergency water treatment.


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An alternative for unknown raw water (characteristics) is ferric chloride as it is also usable in a rather wide pH range. This product can be used as well for assisted sedimentation as for direct rapid sand filtration. With relatively short assisted sedimentation times in emergency treatment and/or when the dosage is incorrect (this for both the assisted sedimentation and the filtration procedures), the water treated with


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FeCl3 might turn (a little) yellowish. Although iron isn’t harmful for people’s health, the beneficiaries might reject the treated water due to its colour and certainly when high residual concentrations render it


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unpalatable. Anyway, it is recommended that the iron (residual) concentration stays within the approved long-term standards, namely 0.2 mg/l.


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Aluminium sulphate is interesting for assisted sedimentation and direct rapid sand filtration, certainly as it can be found nearly everywhere in the world for reasonable prices. Ideally, the pH of the raw water should be between 6.0 and 7.4, because beyond this pH range, the needed amounts of the product rise drastically. It is recommended to buy aluminium sulphate directly under crystallized form because the breaking of lumps into crystals to ease the preparation of the mother solution requires a lot of work and protective clothing (e.g. gloves, mask, goggles).


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There are some unconfirmed studies claiming that “high” aluminium concentrations (within drinking water) might in the long run cause Alzheimer disease and neurological disorders. Potentially more worrying for (emergency) aid-agencies is the unconfirmed concern that malnourished children consuming water with high concentrations of (residual) aluminium might not pick up their weight again. Although that there are still a lot of discussions on the potential adverse health effects of this product, it is important to measure its residual concentration with an appropriate test kit after the water has been treated with a coagulant containing aluminium. The residual aluminium concentration should always be kept as low as possible (ideally less than 0.2 mg/l). In case any of the measurements are outside the normally used standards (indicators), advice should be sought from your technical referent.


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Strict quality control measures need to be respected when purchasing chemicals for potable water treatment (e.g. coagulants, disinfectants). In case of local purchase, contact your technical referent in order to assure that they are fit for human consumption.


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Even though ferric chloride and aluminium sulphate don’t have an expiry date, they should always be stored under correct conditions, meaning a cool dark place with low humidity.


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Several products combining a coagulant, potentially some flocculants, and a disinfectant are available under the form of tablets or sachets. These products are intended for individual household or small scale community water treatment. A certain vigilance is required with these products because fixed doses of different chemicals are added to a determined amount of raw water that can have any quality, without performing a jar test (T.B. 2.15) or a Modified Horrocks test (T.B. 2.21). The Free Residual Chlorine concentration (T.B. 2.22) of the treated water should at least be analysed, and preferably also its residual aluminium or iron concentration (depending on the coagulant used in the product). In case any of the measured values are outside the normally used standards (indicators), advice should be sought from your technical referent. Besides the potential technical issues, a lot of attention should also go to the distribution procedure of these products. It is also important to


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should be sought from your technical referent. Besides the potential technical issues, a lot of attention should also go to the distribution procedure of these products. It is also important to verify if the beneficiaries use the product properly. Hence, a promotion and training campaign will be of utmost importance.


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Measure the pH and the turbidity of the raw water. These analyses can be done with the pool tester (T.B. 2.22) and the turbidity tube (T.B. 2.13).


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Perform additional analyses on the water’s conductivity and alkalinity (pH buffer effect), certainly when the jar test isn’t successful over a wide range of coagulant dosages.


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Place at least 5 one litre transparent measuring beakers (jars) on a flat working space. The advantage of transparent recipients is that the flocks will easily be detectable.


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Inject with a syringe (e.g. 10 ml capacity) a dose of 1% coagulant solution in every beaker, by increasing gradually the amount (e.g. 0.5, 1, 3, 5 and 7 ml). Mark the injected doses on the beakers to avoid confusion afterwards.


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Stir the coagulant thoroughly in a circular movement during about a minute, immediately after the dose has been injected. The stirring can be done with the syringe itself.


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Detect if flocks start to appear in one or more recipients after some time. This process should normally appear before the water stops turning in the beaker. If this is not the case, there is only a small chance that flocks will still form.


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➞ When no flocks have formed in any of the beakers before the water stopped turning, the jar test will have


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to be repeated completely with higher dosages, although there might be other reasons for the raw water not to flocculate (e.g. unfavourable conductivity and/or pH buffer effect).


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➞ When flocks have formed in the beaker with high dosage but not in the jars with lower dosages, the highest dose (e.g. 7 ml) can be added to each of the latter jars (e.g. going to 7.5, 8,10, and 12 ml).


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Compare visually the results in the different beakers (turbidity, size of the flocks, velocity of settling down). The jar with the best results indicates how much coagulant should be added per given amount of raw water. If there is hesitation in between two recipients, the “ideal” dose might probably be in between both of them.


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Fine-tune the dosing around the most favourable values by repeating the jar test completely in the same way as described above. For instance, if the beakers in which 3 and 5 ml of coagulant were injected gave the best preliminary results, the jar test can be repeated with dosages in between these values (3 ml, 3.5 ml, 4 ml, 4.5 ml and 5 ml).


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Compare visually the results in the different beakers (turbidity, size of the flocks, velocity of settling down). It can be tried to pour the supernatant gently in a turbidity tube, without having flocks coming along or breaking up. If it is still difficult to determine the best result because the turbidity of several jars is the same, choose the one where the least coagulant solution was injected. Note that the (field) jar test is only an indicator of how much coagulant solution needs to be added in reality.


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Extrapolate how much coagulant is required for the production of a big amount of water (e.g. 30 m³), based on the “ideal” dose that has been determined by the jar test.


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Jar test indicates 3 ml of 1% Al2(SO4)3 solution per litre of raw water, extrapolated for a 30,000 l tank


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Based on the active ingredient of Al2(SO4)3, 5 kg will be needed for the 90 l (55.6 g/l x 90l; T.B. 2.14).


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As it is often impossible to make mother solutions with polymers (they might start to flocculate already with the water of the solution), these coagulants have to be used under their pure form. This means that the realisation and interpretation of a jar test are extremely difficult due to the very low volumes of these products required to treat turbid water (in the order of 0.01 to 0.15 ml/l of raw water). An insulin syringe (1 ml) could be used to attempt a jar test with 1 litre beakers. As such, the jar test will stay an approximation, but precise enough to start the emergency water treatment.


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Therefore is the jar test for polymers often skipped in emergency situations. Hence, the tests are immediately done in situ, on large scale. Anyway, polymers are mostly less critical in their dosing in comparison with coagulants like aluminium sulphate or ferric chloride. Nevertheless, regular residual aluminium / iron concentration analyses should be done on the treated water.


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In practice, foresee about 0.5 to 3 l of liquid polymers per reservoir of 30 m³. Be aware that these values are only an indication in which range large scale tests should be made.


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Measure the pH and the turbidity of the treated water by means of the pool tester (T.B. 2.22) and the turbidity tube (T.B. 2.13). These tests are actually the pre-tests for chlorination (Modified Horrocks test) (T.B. 2.21 and 2.22).


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Analyse the residual metal concentration, depending on the coagulant being used (iron or aluminium). Their concentration should normally be lower than 0.2 mg/l. Be aware that the concentrations after a field jar test and emergency assisted sedimentation are often up to 10 times higher.


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RemarksIf transparent beakers aren’t available, big glasses (e.g. pints), glass jars or even plastic buckets with all the same and known volume can be used as well. During the jar test, the injected doses of coagulant will have to be adapted according to the volume of the recipients.The thorough stirring immediately after the coagulant has been injected in the raw water is important to have a homogeneous mixture. This avoids over- and under-dosing at different places in the recipient, and enhances the formation of flocks. Under laboratory conditions, once the thorough stirring is done, a slow mixing at specific speeds will continue by an electric apparatus for 20 minutes. As this is very difficult to achieve manually on the field, the slow mixing is limited until the swirl after the thorough stirring stops. This isn’t ideal, but it still gives a good indication of the required coagulant dosage.When the alkalinity (pH buffer effect) of the raw water is low, its pH can drop significantly


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stirring stops. This isn’t ideal, but it still gives a good indication of the required coagulant dosage.When the alkalinity (pH buffer effect) of the raw water is low, its pH can drop significantly when coagulants are added, as most of them are acid. This can have a serious influence on the quantity of coagulant needed, certainly when aluminium sulphate is used. A low pH buffer effect could even hamper the coagulation / flocculation process. The pH of the raw water can be adapted (made higher or lower) with certain products (e.g. respectively lime or sulphuric acid), but due to its specific difficulties (e.g. dosing, safety), advice from your technical referent should be sought.A very low concentration of ions (low conductivity) in the raw water can cause problems as well with the coagulation / flocculation process. Rendering the conductivity a little higher by adding some kitchen salt might solve the problem, but it is recommended to contact your technical referent for further


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/ flocculation process. Rendering the conductivity a little higher by adding some kitchen salt might solve the problem, but it is recommended to contact your technical referent for further information.The presence of high quantities of algae or other organic material that can be found in swamps for example, might require the use of a lot more coagulant.


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Install the sedimentation reservoir preferably at a spot nearby the raw water source, but far enough to avoid that is gets flooded when the water level would (suddenly) rise. Make sure that the reservoir is installed on a solid and horizontal “platform” for security reasons.


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➞ In emergency situations, onion tanks or big (circular) tanks with a metallic frame and plastic lining are the


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easiest and fastest to install (T.B. 2.35; 2.36). These reservoirs should have a useful height of at least 1 m.


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➞ Reservoirs with metal sheeting as a support can be used as well, but it takes longer to install them (T.B.


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Install a motor pump with its needed accessories (e.g. strainer, suction and delivery pipes; T.B. 2.28).


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Add the coagulant (solution) in proportional quantities (as determined by the jar test; T.B. 2.15) during the time the tank is filled with raw water,. The coagulant can be added to the raw water in various ways:


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The principle of this system is that the coagulant gets mixed by simply being dropped into the raw water spouting out of the pump’s delivery pipe (as per figure A). The advantage is that only a plastic recipient with a tap to regulate the coagulants flow is required. The recipient should be installed on some kind of platform, together with the delivery pipe. The delivery pipe should be oriented tangential to the reservoir in order to create an internal circular movement of the coagulated water, which will improve the flocculation process. However, the water falling into the reservoir might break the flocks already forming in the rotating water (certainly when the reservoir is still rather empty).


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When liquid polymers are used as coagulant, a 20 l jerrycan with tap can be sufficient as recipient. Its dosing can be fine-tuned to some extent by adding an infusion set, if available.


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Rather big quantities of aluminium sulphate or ferric chloride solutions will be required, thus a bigger recipient (e.g. 120 l jar for cholera interventions) or several jerrycans will be needed.


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This device, equipped with a regulation valve and a small flow meter, is installed at the entrance of the pump (as per figure B), so the coagulant solution can be “sucked” up proportionally to the raw water flow. The “flash” mixing of both liquids by the impellor of the pump enhances the coagulation process. The 90° elbow (as per figure C) allows the coagulated water to arrive in a circular movement at the bottom of the reservoir, which will improve the flocculation process, and without breaking the already existing flocks. All these factors result in an enhanced reduction of the turbidity.


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Turn the regulation valve of the SSD system in such a position that its flow is set at 100 l/h (indicated by the SSD flow meter).


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Allow the flocks to settle down at the bottom of the tank, once the reservoir is completely filled. This might take several hours.


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Retrieve the clarified water with great care. Settled flocks can be pumped up when the flow rate is too high or when the entrance of the retrieval pipe comes too close to the sludge at the bottom of the reservoir. Sometimes, the flocks might float on the water surface. In this case, the clarified water has to be retrieved from underneath them. To deal with these problems, a retrieval pipe with floater can be connected to an outlet at the inside of the reservoir (as per figure C). This also allows the removal of the treated water by gravity in a safe way. This principle is strongly recommended if an onion tank is used for sedimentation.


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Assisted batch sedimentation is an appropriate treatment method in the first phase of an emergency or as pre-treatment before filtering, because it requires a limited amount of material. However, depending on the settling time of the flocks, several reservoirs in parallel might be needed to come to the required water production rate.


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Bladder tanks should not be used for (assisted) sedimentation because their shape doesn’t allow a circular movement of the coagulated water and it would be difficult to retrieve the treated water without having flocks coming along. Because they are completely closed, it would also be difficult to remove the sediments afterwards.


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Besides the described batch procedure, the assisted sedimentation can also be done continuously by inclined plate sedimentation or up-flow clarification for instance.


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Polymers have better performances for assisted sedimentation in comparison with the other coagulants used on the field. But as they are used undiluted (related to the difficulties to make a mother solution), polymers are more difficult to dose. Coagulants such as aluminium sulphate and ferric chloride are introduced in the raw water as a diluted solution (mostly 1% mother solution), thus their dosing is less difficult (T.B. 2.14).


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A further treatment method, at least a disinfection of the water, must follow the assisted sedimentation process. Be aware that assisted sedimentation will not eliminate all cysts nor all helminths eggs, neither will chlorine. Hence, it is also recommended to filter the water before chlorination, certainly where very good quality water is required (e.g. health structures).


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With the rather short sedimentation times available during emergencies, the treated water often has high residual concentrations of metal coagulants (the standard is 0.2 mg/l, but in reality it is often up to 10 times higher). Field test kits for measuring the aluminium / iron residual concentration should be available to do a regular follow up of the treated water.


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These high residual metal concentrations due to the coagulants might have a negative impact on the health of vulnerable people (e.g. severely malnourished children) or on the consumers’ acceptability of the water (colour, taste). These residual metal concentrations can be reduced by (rapid sand) filtration.


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The sludge doesn’t have to be removed after every cycle as it helps to form flocks during the next batch (certainly if the turbidity of the raw water is rather low). However, as the sludge layer thickens, the water production per cycle reduces. Therefore is it necessary to clean the reservoir at regular intervals. This can be done manually by putting the flocks in suspension (e.g. with soft brooms) during the draining of the reservoir or by means of a motor or even better a dewatering pump (T.B. 2.25).


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To preserve the environment, a sedimentation hole should be dug for the drained water to pass through. If the retention time in the hole is long enough, the flocks can settle down. Initially, it’s possible that the drained water will even infiltrate in the underground, but after a while the soil will certainly be saturated. The “overflowing” water should be drained back to the surface water, but down-flow of the intake of the raw water pump.


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The Suction Side Dosing system cannot be used for liquid polymers, because its regulation isn’t fine enough for the undiluted product. There is also the risk that the aggressiveness of certain polymers would destroy the seal of the pump axle.


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All systems based on support / surface filtration function in a similar way: the water has to pass through a surface with very fine pores, which will retain the particles that are bigger than the pores. These filters are effective, but do clog rapidly when the turbidity of the water is high. Thus they need to be cleaned regularly, and some systems even need a frequent replacement of the filters. Typical examples of surface filtration are cartridge and membrane filters.


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The raw water passes through cartridges, made of metals, fibres or ceramic material, with a fine porosity. Particles in suspension, cysts, helminth (eggs), most bacteria and a certain range of viruses will be retained. Therefore, the treated water is of good quality. However, turbid water will clog the filters rather rapidly as the particles settle down on their surface (the higher the turbidity, the faster the clogging). Even with a low turbidity, the cartridges have to be cleaned frequently, certainly when they are pressurised.


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Ceramic candles (T.B. 2.18) are most often used for individual and household water treatment, due to their low production rate. They are mainly found in survival kits, in expatriates’ houses and sometimes in (small) health structures. Under certain circumstances however, they might also be the preferred choice for a population to do their own household water treatment. As the abrasive cleaning of the candles with a brush or a rough sponge has to be done rather often, they need to be replaced frequently (ideally every 6 months and at least once a year).


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This filtration method consists of permeable membranes, often rolled up in tubes which are stored in cylindrical containers. The kind of filtration (micro-, ultra- or nano-filtration) is determined by the size of the membrane pores. As the pores are extremely fine, suspensible particles, cysts, helminth eggs and bacteria can be retained, even viruses when ultra- or nano-filtration membranes are used. However effective this kind of filtration is, post-chlorination is still strongly recommended to have a remnant protection effect. As these kinds of systems function on the surface filtration principle, they have a tendency to clog rather rapidly, certainly with a high turbidity. So (very) regular backwashes with clean water are necessary, but these are often managed automatically. Producing very high quality water without the need of chemicals (except for the recommended post-chlorination and some acids / alkalis for cleaning once in a while), these filtration systems are unfortunately


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very high quality water without the need of chemicals (except for the recommended post-chlorination and some acids / alkalis for cleaning once in a while), these filtration systems are unfortunately also very expensive and the membranes are still rather fragile.


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Reverse osmosis is also associated to the membrane technology. In this case, (extreme) high pressures are used to remove even dissolved elements like salt out of the water. These systems are not at all adapted for turbid water. Small scale forward osmosis filters for pathogen removal are also available. Their driving force to filter the water does not come from hydraulic pressure (pump, gravity), but from osmotic pressure.


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In this process, the suspensible material is stopped in the inter-granular spaces of the filtering material (often sand). In general, two treatment methods on a granular bed principle are commonly used: slow and rapid sand filtration. Slow sand filtration is a mechanical and microbiological process. Rapid sand filtration is only a mechanical process, which is also based on sieving but mainly on the principle of adsorption.


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The mechanical filtering action of the granular sand bed together which the biological membrane that will develop on top after some time (named Schmutzdecke) can remove cysts, helminth eggs, a large part of the bacteria and even some viruses from the water. It gives also good results in clarifying the raw water, as long as it doesn’t contain too many particles in suspension. Slow sand filtration isn’t suited to deal with turbidities above 30 NTU. In case the turbidity is above this level, the raw water should pass through roughing filters, which is actually a system of natural sedimentation. A post-chlorination of the water leaving the slow sand filters is always recommended to obtain a remnant effect.


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However simple the process seems, there are some limits. As the velocity is low (0.1 - 0.3 m/h), the head losses stay low, so that the filtration can be done by gravity. On the other hand, big filters are required to obtain a sufficient water production for a large population (e.g. a surface of 20 m² will produce a flow of 2 to 6 m³/h). The system has to run 24 hours a day to guarantee the water quality. After maintenance work is done, it will take at least several days for the Schmutzdecke to reform itself, and the pathogens won’t be removed over that period. To overcome this problem, two parallel slow sand filters need to be installed and maintained alternately. Another option is to build a big storage reservoir, which can only be filled if the daily production of the slow sand filter is (a lot) higher than the required daily demand.


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As the production capacity is rather low, slow sand filtration isn’t often used in emergencies. Contact your technical referent before taking the decision to implement such a filtration system.


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A rapid sand filter operates on two principles; some mechanical straining and mainly physical adsorption on the surface of the sand grains. Rapid sand filtration can be installed after an assisted sedimentation process to remove the flocks (including the bacteria and viruses trapped inside), cysts and helminth eggs that would have escaped otherwise. The rapid sand filter will also be able to remove the coagulation residuals (e.g. iron or aluminium). This gives good quality water, but needs three different steps with the post-chlorination included.


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Direct assisted rapid sand filtration is possible as well; a coagulant will be added and the flocks will be filtered out directly without sedimentation in a reservoir first. This process will remove the coagulants’ residuals to acceptable concentrations (possibly even less than 0.2 mg/l, which is the maximum standard), reduce very efficiently the turbidity of the raw water (< 5 NTU) and retain most helminth eggs and cysts. However, the turbidity of the raw water should not exceed 300 NTU, because the filtration periods will become too short and backwashing will be needed too often. In such situations, it is recommended to add assisted sedimentation (in batch or continuous) prior to the filtration step.


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According to the application, rapid sand filtration is done with velocities going from 4 up to 50 m/h, thus a (relatively) high water production is possible with small filters. Several filters with filtration beds of different granulometry can be put in series to obtain a better reduction of the turbidity over longer filtration periods. The backwashes of the filters are done with pre-filtered or completely treated water, but compressed air, as used in big water treatment plants, is often abandoned for small field treatment units because of the complexity and extra expenses.


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As the contact time in between the water and the sand is short, it’s impossible to have the biological action that appears in slow sand filtration. Thus the free bacteria and viruses that aren’t trapped in the flocks won’t be eliminated by rapid sand filtration, and post-chlorination becomes obligatory.


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Direct rapid sand filtration is a frequently used principle for field water treatment kits. This is due to the production of potentially large quantities of high quality water (in combination with post-chlorination and possibly pre-sedimentation) for rather low purchase costs and low operation and maintenance expenses.


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Gravity filter: One recipient containing several candles stacks on the top of another, which is collecting the treated water. By filling the upper recipient, the water will pass drop-by-drop through the candles (provided they are not clogged) into the lower container. The filtered water can immediately be taken from the tap at the lower recipient.


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Pump filter: In this case, the water is forced under pressure through the filter by means of a small integrated hand pump, thus increasing the flow. The strainer of its plastic “suction” pipe should be put into the raw water before the pumping starts.


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Assemble the candles of the gravity filter correctly with their rubber washers placed in between the candle and the internal base of the upper container and their nuts properly tightened to ensure that no water can pass without being filtered.


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Keep the container where the filtered water is collected and preserved closed. It should be cleaned at least once a week with a 0.05% chlorine solution (T.B. 2.20) and rinsed afterwards with filtered water, without touching the inside of the container.


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Brush the candles under clean running water when their flow becomes too weak, rinse them and reassemble the filter (see manufacturer’s instructions). A specific brush or rough sponge should be included in the kit, but in case this specific cleaning material isn’t available, a semi-hard non-metallic brush specially dedicated for this use can be utilized as well. As the candles are fragile, handle them with care.


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Clean and air-dry the (pump) filters completely when they won’t be used over prolonged periods (e.g. weeks to months). This avoids fungus and bacteria growth inside, which could lead to illness when the filter is put back into service.


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most often found as granules (also existing as powder or tablets)	 Sodium DiChloro-isoCyanurate or NaDCC :


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Store chlorine-generating products in their original packaging which should be airtight, non-metallic or properly painted / enamelled recipients. Shelter these products from heat, light and humidity, and store them in a restricted access area (chlorine is dangerous especially for children). Never store chlorine-generating products together with organic matter, nor with combustibles because of the high risk of fire or explosion. For quantities larger than 10 kg, look for a separate storage place, away from equipment that could be damaged by corrosion.


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All chlorine-generating products have a loss in their chlorine content over time, and they generate toxic and corrosive chlorine gas, which is heavier than air. Thus storage places for chlorine-generating products should be equipped with ventilation at ground level. Never store chlorine-generating products in cellars.


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➞ Particularly chlorinated lime and all forms of sodium hypochlorite are unstable. Sodium hypochlorite solutions should not be used if they have been stored for more than 3 months after being manufactured.


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➞ Calcium hypochlorite stores better with an active ingredient loss of about 2 - 5% per year under appropriate storage conditions. But under tropical conditions, the loss is usually much higher and the recommended


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➞ NaDCC is by far the most stable product. Manufacturers guarantee a stable chlorine content (expiry date) of 2 years for granules, 3 years for tablets in unopened tubs and 5 years for strips, under appropriate storage conditions.


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Any chlorine-generating product may be fatal if inhaled or swallowed. It is harmful if absorbed through the skin as it causes severe irritation. High chlorine concentrations are extremely destructive to the mucous membrane tissues, upper respiratory tract, eyes and skin. In case of contact with the eyes, rinse immediately with plenty of clean running water and seek medical advice.


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When handling any chlorine (-generating) product (e.g. opening drums, preparing and/or manipulating solutions), use a sheltered but well ventilated location and wear suitable protective gear such as rubber gloves, a plastic apron and eye / face protection.


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Never mix calcium hypochlorite with NaDCC because toxic and explosive tri-chloramine gas may be generated.


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When purchased locally and in large quantities, calcium hypochlorite often comes in 40 - 50 kg drum containers. All containers should always be stored in the upright position. They should not be dropped, rolled or skidded in any case due to the risk of fire and explosion.


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When measuring calcium hypochlorite or NaDCC granules, only use a plastic, glass or enamelled measuring device which is completely clean, dry and free from any foreign matter, because of the risk of fire and explosion.


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Chlorine-generating products should not be brought into contact with acids, vinegar, toilet bowls cleaning agents or any other cleaning agents (e.g. detergents) due to the risk of releasing toxic chlorine fumes. Contact should also be avoided with beverages or any combustible material including paper, rags, tobacco, oil based products and any form of heat like matches, flames, lighted cigarettes because of the risk of fire and explosion.


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When chlorine-generating products are spilled, wash them thoroughly down with water and do not allow them to remain in contact with any organic or combustible matter like cloth, paper, oil.


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Determine the weight of the chlorine-generating product that is required to make 1 l of solution, using the following formula:


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With X = grams of product to be added per litre of water to reach the desired solution concentration (g/l) Y = desired solution concentration (%)


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N = 10 g/l, equal to the amount of pure chlorine (active ingredient 100%) needed to make 1 litre of 1% mother solution


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(calculation: 1 l of water weighs 1000 g; 1% of 1000 g = 10 g, thus 1% solution = 10 g/l) C = concentration of the product’s active chlorine, as mentioned on the packaging (%)


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Pour the required weight of chlorine-generating product in the determined amount of clean water. The opposite (water on chlorine) is not allowed as this can induce violent chemical reactions.


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Make 1 litre of 1% mother solution with Sodium DiChloro-isoCyanurate (NaDCC) granules containing 55% active chlorine


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From liquid chlorine-releasing compounds: sodium hypochlorite (bleach) having 4 or 5% active chlorine, sodium hypochlorite concentrate having 15% active chlorine.


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Determine the total parts of water that are required in which the sodium hypochlorite needs to be dissolved, according to the following formula:


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add 0.2 l of concentrated solution to 0.8 l of water (1 l of solution/5 parts = 0.2 l of bleach; thus 0.2 l of bleach x 4 parts of water = 0.8 l of water).


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➞ Take one part concentrated solution and add to 74 parts of water. In this case, add 13 ml of concentrated solution to 987 ml of water


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For chlorinating drinking water, a 1% chlorine mother solution (also called stock solution) is prepared first, whichever chlorine-generating product is used. The tables hereunder present the procedures to prepare a 1% mother solution starting from different chlorine-generating products. The quantity of 1% mother solution that needs to be added to disinfect a measured volume of water is then determined by the modified Horrocks test (T.B. 2.21).


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<table><tr><td>Starting with</td><td>Preparation</td><td>Remarks</td></tr><tr><td>Calcium hypochlorite (HTH®)</td><td>15 g per l of water</td><td>Let the calcium deposit settle</td></tr><tr><td>with 65 - 70% active chlorine</td><td>or</td><td>and use only the supernatant</td></tr><tr><td/><td>1 level scoop/l (1 soupspoon/l)</td><td/></tr><tr><td>Sodium DiChloro-isoCyanurate</td><td>10 tablets per l of water</td><td>Ensure that the excipients in the</td></tr><tr><td>(NaDCC) with 1 g active</td><td/><td>tablets are non-toxic</td></tr><tr><td>chlorine per tablet</td><td/><td/></tr><tr><td>Sodium DiChloro-isoCyanurate</td><td>18 g per l of water</td><td>Ensure that the excipients in the</td></tr><tr><td>NaDCC) granules with 55%</td><td/><td>granules are non-toxic</td></tr><tr><td>active chlorine.</td><td/><td/></tr></table>


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Starting with Preparation Remarks Calcium hypochlorite (HTH®) 15 g per l of water Let the calcium deposit settle with 65 - 70% active chlorine or and use only the supernatant 1 level scoop/l (1 soupspoon/l) Sodium DiChloro-isoCyanurate 10 tablets per l of water Ensure that the excipients in the (NaDCC) with 1 g active tablets are non-toxic chlorine per tablet Sodium DiChloro-isoCyanurate 18 g per l of water Ensure that the excipients in the NaDCC) granules with 55% granules are non-toxic active chlorine.


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Chlorinated lime with 30%	33 g per l of water	Let the lime deposit settle active chlorine	 or 2 level soupspoons/l	and use only the supernatant


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Sodium hypochlorite (bleach)	200 ml per l of solution with 5% active chlorine	 or 1 volume of bleach for


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Sodium hypochlorite (bleach)	250 ml per l of solution with 4% active chlorine	 or 1 volume of bleach for


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Different solutions with different chlorine concentrations are used in health structures. The chlorine concentration in the solution depends on the usage of the disinfecting solution. These solutions are essential to maintain a hygienic and safe environment within a health structure and even more during outbreaks of infectious diseases like cholera, shigellosis, Ebola or Marburg. An in-depth description of how to use these solutions properly for these highly infectious diseases can be found in the respective guidelines (section 8.5 Further reading).


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The 6 main chlorine solutions are: 2%, 1%, 0.5%, 0.2%, 0.1%, 0.05%. They can be prepared by using the formulas presented above. In the context of these guidelines:


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<table><tr><td>2%</td><td>Disinfection of corpses in case of a cholera outbreak Disinfection of stools and vomit in case of a cholera outbreak</td><td>T.B. 8.01</td></tr><tr><td>1%</td><td>Used as a mother solution to be diluted for: disinfecting drinking water other purposes like cleaning and disinfection of a: - well</td><td>T.B. 2.21; T.B. 2.23 T.B. 2.03</td></tr><tr><td/><td>- flexible reservoir</td><td>T.B. 2.37</td></tr><tr><td>0.5%</td><td>Disinfection of corpses in case of Viral Haemorrhagic Fevers</td><td>T.B. 8.01</td></tr></table>


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2% Disinfection of corpses in case of a cholera outbreak Disinfection of stools and vomit in case of a cholera outbreak T.B. 8.01 1% Used as a mother solution to be diluted for: disinfecting drinking water other purposes like cleaning and disinfection of a: - well T.B. 2.21; T.B. 2.23 T.B. 2.03 - flexible reservoir T.B. 2.37 0.5% Disinfection of corpses in case of Viral Haemorrhagic Fevers T.B. 8.01


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Disinfection of stools, vomit, urine, body fluid spills, gloved hands in case of Viral Haemorrhagic Fever outbreaks


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0.2%	• Disinfection of floors, walls, surfaces, beds, objects, latrines in case of a cholera outbreak


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<table><tr><td>0.1%</td><td>Disinfection and cleaning of: - tankers, pipes, pumps</td><td>T.B. 2.34</td></tr><tr><td/><td>showers washing facilities collective dustbins and drainage holes reusable sharps containers drop pipe, slab and surroundings of a sharps pit soft waste bins organic waste bins and the slap of an organic waste pit</td><td>T.B. 4.01 T.B. 4.02 T.B. 5.01 T.B. 6.01 T.B. 6.02; T.B. 6.03 T.B. 6.05; T.B. 6.06 T.B. 6.08</td></tr><tr><td>0.05%</td><td>Scrubbing the walls of a well Disinfection and cleaning of: - recipients of ceramic candle filters</td><td>T.B. 2.03 T.B. 2.18</td></tr><tr><td/><td>open tanks lorries / carts (waste transportation)</td><td>T.B. 2.37 T.B. 5.03</td></tr></table>


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0.1% Disinfection and cleaning of: - tankers, pipes, pumps T.B. 2.34 showers washing facilities collective dustbins and drainage holes reusable sharps containers drop pipe, slab and surroundings of a sharps pit soft waste bins organic waste bins and the slap of an organic waste pit T.B. 4.01 T.B. 4.02 T.B. 5.01 T.B. 6.01 T.B. 6.02; T.B. 6.03 T.B. 6.05; T.B. 6.06 T.B. 6.08 0.05% Scrubbing the walls of a well Disinfection and cleaning of: - recipients of ceramic candle filters T.B. 2.03 T.B. 2.18 open tanks lorries / carts (waste transportation) T.B. 2.37 T.B. 5.03


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RemarksChlorine reacts with metals, leading to a high chlorine consumption and a strong oxidation of the metals. Hence, never prepare chlorine solutions in metallic containers (unless properly enamelled).Chlorine must always be poured in the water, but the opposite (water on chlorine) is prohibited due to the risk of violent exothermic reactions that could lead to serious injuries.The use of chlorinated lime, sodium hypochlorite containing 4 - 5% active chlorine or sodium hypochlorite concentrate containing 15% active chlorine is only recommended if NaDCC and HTH® are not available.A 2% chlorine solution should only be used for restricted purposes and should never be sprayed in enclosed facilities because of its high concentration and the risks associated with the release of toxic chlorine gas in contact with the air or organic matter.Chlorine solutions should not be poured into a toilet or a latrine as it will stop the natural decomposition in the septic tank or pit, filling them up


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gas in contact with the air or organic matter.Chlorine solutions should not be poured into a toilet or a latrine as it will stop the natural decomposition in the septic tank or pit, filling them up more rapidly and generating extremely bad odours. However, in isolation units during epidemics of cholera, shighela, Ebola or Marburg, it is recommended to use chlorine solutions to disinfect all the patients’ excreta (section 8.5 Further reading).Calcium hypochlorite (HTH®) and chlorinated lime leave a deposit, thus only the supernatant should be used and the deposit disposed of in a shallow pit.Less corrosive products exist to disinfect medical equipment or surfaces in long-term health structures.


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To determine how much 1% chlorine mother solution that needs to be added to a measured volume of water, use the modified Horrocks test:


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Measure the pH of the water to be treated in order to determine the needed contact time (T.B. 2.22).


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Take at least 4 non-metallic containers of known volume (preferably 20 l plastic buckets or jerrycans), all having a cover.


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Clean the containers and their cover 3 times with the water to be treated. When the containers are soiled inside, the dirt can be removed the first time by a clean brush (or clean hands when they fit inside) and water, the remaining times only rinse with the water.


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Fill all the containers with the same amount of water to be treated (e.g. 20 l), put their cover on and label them (1 to 4).


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Add to each bucket a progressively increasing dosage of 1% chlorine mother solution with a graduated sterile syringe :


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➞ If the pH < 8, choose as reference the container where the Free Residual Chlorine concentration is between 0.2 and 0.5 mg per litre. In case two following containers would have a FRC in between 0.2 and


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➞ If the pH > 8, choose as reference the container where the FRC concentration is between 0.4 and 1.0 mg per litre. In case two following containers would have a FRC in between 0.4 and 1.0 mg/l, opt for the one with the highest concentration.


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Repeat the Modified Horrocks test with higher 1% mother solution dosages if none of the FRC measurements are in between 0.2 - 0.5 mg/l (0.4 - 1.0 mg/l; depending on the pH).


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Extrapolate the determined dose of 1% mother solution to the volume of the water reservoir that will be used.


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Pour the solution in the reservoir, ideally while filling it up to obtain a homogenous repartition of the solution in the water and mix well (if still needed).


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Control the FRC at the level of the taps before the water is distributed to the beneficiaries. Slightly adjust the reservoir’s mother solution dosage, if needed.


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The pH is measured to be 7.2 and the water temperature is at 20 °C. The FRC levels of the water in the containers are measured after the required 30 minutes contact time, and are respectively as follows:


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<table><tr><td>Container</td><td>Added 1% mother solution</td><td>Measured FRC concentration</td></tr><tr><td>1</td><td>1.0 ml</td><td>0.0 mg/l</td></tr><tr><td>2</td><td>1.5 ml</td><td>0.1 mg/l</td></tr><tr><td>3</td><td>2.0 ml</td><td>0.4 mg/l</td></tr><tr><td>4</td><td>2.5 ml</td><td>1.0 mg/l</td></tr></table>


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Container Added 1% mother solution Measured FRC concentration 1 1.0 ml 0.0 mg/l 2 1.5 ml 0.1 mg/l 3 2.0 ml 0.4 mg/l 4 2.5 ml 1.0 mg/l


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The chosen reference dose will therefore be the one of recipient number 3, because its obtained FRC concentration of 0.4 mg/l is between 0.2 - 0.5 mg/l.


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If 2 ml of 1% chlorine solution is needed to chlorinate 20 l of water at the correct dosage, then 100 times as much 1% mother solution will be required to chlorinate 2,000 l of the same water quality, thus 100 x 2ml


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The doses of 1% mother solution given in this example are only an indication. It may happen that the chlorine amount needed to treat the water in the field is very different from this example.


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Chlorination is effective against most enteric bacteria and plenty but not all viruses (e.g. Hepatitis E). At the doses normally used for potable water treatment, chlorine isn’t really effective against protozoan cysts and helminth eggs.


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The most practical way to guaranty chlorine’s best effectiveness is to monitor the pH, the turbidity and the Free Residual Chlorine concentration after the optimum contact time. Note that the chlorine demand may vary over time with (unexpected) changes in the amount of organic matter in the water. It is thus important to monitor the FRC concentration, the pH and the turbidity frequently in order to be able to adjust the water treatment accordingly.


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Particles in suspension (turbidity) can protect micro-organisms from chlorine disinfection. Even with a correct Free Residual Chlorine concentration, many harmful micro-organisms may survive. Water to be chlorinated must contain as little visible suspensible material as possible and when measured (e.g. with a turbidity tube; T.B. 2.13), it should be less than 5 (N)TU (less than 20 (N)TU in acute emergencies). If the turbidity exceeds the recommended values, a pre-treatment such as sedimentation (natural or assisted; T.B. 2.14; 2.15; 2.16) or filtration (T.B. 2.17) should be done before the chlorination process.


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Chlorination is less effective if the pH of the water is above 8 (T.B. 2.22), therefore a doubling in contact time (60 minutes) and FRC (0.4 - 1.0 mg/l) is required. If the temperature is below 10 °C, the contact time should also be doubled (60 minutes), but the Free Residual Chlorine concentration should still be between


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If recipients with a tap are used, do not use the tap to fill the pool tester, as it might be contaminated and lead to false results.


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The taste or odour of chlorine in water is not a proof of the presence of Free Residual Chlorine (FRC). It could be due to the presence of Combined Residual Chlorine (CRC), which has a less disinfecting capacity and which cannot be measured with DPD 1 tablets. The CRC can be determined as follows:


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➞ Add an additional DPD 3 tablet in the compartment in which a DPD 1 tablet has already been dissolved


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A verification of the TRC and CRC once in a while is recommended, certainly if NaDCC is used as chlorine-generating product (T.B. 2.19).


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The simplest way to monitor the effectiveness of chlorination is to measure the Free Residual Chlorine (FRC) concentration in the drinking water. The presence of FRC in the treated water (after 30 or 60 minutes contact time, depending on its pH and temperature) indicates that enough chlorine has been added to satisfy the chlorine demand and to create Combined Residual Chlorine (CRC), whilst still leaving an excess of available free chlorine. The remaining FRC is available to deal with possible recontamination in the distribution system or during handling.


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The measurement of Free Residual Chlorine (FRC) concentration and pH is most easily done using a comparator, commonly called a “pool tester”.


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Rinse the inside of the pool tester, including its lid, 3 times with the water to be tested. This is to be sure that all remaining residues of previous tests are removed.


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Fill the 3 compartments to the top with the water to be tested, without dipping it in its recipient.


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Tear the foil strip open and put one Phenol Red tablet in the small left hand compartment without touching it. This is to measure the pH.


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Tear the foil strip open and put one DPD 1 tablet in the small right hand compartment without touching it. This is to measure the Free Residual Chlorine.


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Replace the lid tightly with the arrows pointing towards the coloured reference scale. It is normal that some liquid is pressed out of the pool tester.


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Shake gently until the tablets are completely dissolved. This may take about 20 seconds, depending on the water temperature.


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Read the results immediately in natural day light, comparing the colours in the outer compartments (containing the water samples with the dissolved tablets) with the colour scale of the central compartment (reference).


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Empty the pool tester and rinse it again with clean disinfected water to remove the residues of the analysis, in order to prevent inaccurate results at the next measurement.


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Measuring a Free Residual Chlorine concentration after the required contact time is a good indicator that the chlorination is complete:


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➞ A part of the added chlorine has combined with certain elements in the water (mainly nitrogen) and forms the Combined Residual Chlorine (CRC), which isn’t effective to react rapidly against a post-contamination.


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➞ The remaining residual chlorine is free in the water (FRC) and will immediately react with a post-contamination (remnant effect). The following results should be obtained in low-income countries.


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<table><tr><td>Water characteristics</td><td>Contact time</td><td>FRC</td></tr><tr><td>pH &lt; 8</td><td>30 minutes</td><td>0.2 - 0.5 mg/l</td></tr><tr><td>pH &gt; 8</td><td>60 minutes</td><td>0.4 - 1.0 mg/l</td></tr><tr><td>Temperature &lt; 10 oC (pH &lt;8 )</td><td>60 minutes</td><td>0.2 - 0.5 mg/l</td></tr></table>


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Water characteristics Contact time FRC pH < 8 30 minutes 0.2 - 0.5 mg/l pH > 8 60 minutes 0.4 - 1.0 mg/l Temperature < 10 oC (pH <8 ) 60 minutes 0.2 - 0.5 mg/l


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The required contact time is needed to allow the completion of the disinfection process. The FRC concentration shouldn’t be too low in order to provide a good protection against post-contamination. It shouldn’t be too high either as this might induce the refusal of the beneficiaries to consume the water (not used to the odour or taste of chlorinated water, although they can also be caused by the CRC).


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WARNING: a Free Residual Chlorine concentration above 10 mg/l can cause bleaching of the DPD colour (no colour to be observed), wrongly indicating zero residual chlorine.


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The pool tester can be used as well to perform the modified Horrocks test (T.B. 2.21), as for monitoring the Free Residual Chlorine (FRC) concentration of an operational water supply system.


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The monitoring of FRC for a water supply system should be done on a regular basis (at least daily). It is recommended to let the water flow for a few moments (e.g. 30 seconds) before taking it from a tap. If this monitoring shows a constant discrepancy between the actual results and the expected range, another modified Horrocks test must be undertaken.


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It’s important that the quality of the water to be tested doesn’t change during the rinsing and filling steps of the modified Horrocks test (T.B. 2.21), as this might result in false measurements.


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➞ The water can be taken from the recipient and introduced to the pool tester by means of a sterile syringe


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(e.g. 50 ml). The Free Residual Chlorine would react immediately with a contaminated syringe, thus indicating a lower FRC concentration than is actually present in the treated water. It is therefore of utmost importance not to touch the outside of the syringe that comes in contact with the treated water, nor to place it on a contaminated surface (put it carefully back in its packaging).


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➞ An alternative to the sterile syringe is to gush the water from the water container directly into the pool tester. This is a rapid manner, but a lot of water will be spilled, meaning the whole procedure, including the rinsing and filling of the containers, will have to be repeated if the first round of the modified Horrocks test doesn’t provide acceptable results.


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➞ If recipients with a tap are used, do not use the tap to fill the pool tester, as it might be contaminated and lead to false results.


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For the same reason should the tablets, the inside of the pool tester or the inside part of its cover never be touched. Never use tablets that have fallen on the ground.


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The printing “DPD 1” / “Phenol Red” on the foil strips must be in green, meaning that the tablets are rapid dissolving. Tablets of foil strips with black printing should never be employed with the standard pool tester that is used on the field for monitoring chlorination.


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The tablets normally have a shelf life of minimum 5 years. The expiry date should be printed on the outside of their outer (cardboard) packaging, and for some brands on the foil strips. Other brands have the manufacturing date indicated on the foil strips under the form of a code: “A” is the year 2003, “B” is 2004. The two numbers after the capital letter indicate the manufacturing month.


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Only whole tablets must be used. Do not use broken tablets (bad storage or while opening packaging).


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Do not use tablets that disintegrate on opening or have lost their colour (dull grey / brown instead of bright white for DPD 1, and dull brown instead of bright orange for Phenol Red).


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Read the results within 60 seconds once the tablets have dissolved to be sure of a reliable measurement. The results are not guaranteed after this limited period.


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Read the results under good illumination conditions, meaning natural day light. Sun glasses must be taken off. Ideally, the reading should be made on a white surface (e.g. a tent wall), but pointing the pool tester towards the sky, away from the sun, can do as well.


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The pH must systematically be measured before starting chlorination, as a pH > 8 requires a higher contact time and a higher FRC concentration (see above). The pH of (surface) water may vary significantly over time, so it needs to be controlled frequently.


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➞ pH values under 6.8 will always cause a yellow colouration, whereas pH values above 8.2 will cause a red colouration with the Phenol Red method of the standard pool tester used on the field.


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Set up the bucket chlorination system by training several chlorinators and their supervisors. Typically one supervisor can manage a maximum of 30 chlorinators, although this will vary according to the situation. In practice, one chlorinator should be able to treat at least 2 buckets of water per minute.


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Providing basic information on chlorination to the beneficiaries; e.g. the need to wait for 30 minutes before using the water (if pH < 8).


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Responsible for the chlorination teams and for the promoting team (promotion of the chlorination system to the beneficiaries).


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Monitoring the performance of the chlorinators; checking of the chlorinators’ records and (randomly) spot checking the chlorinated water inside the users’ recipients through Free Residual Chlorine measurements.


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Locate the chlorinators next to areas where people collect drinking water. In areas where there are many water points, try to organise with the community a smaller number of focal water points that are accessible to all and that can provide enough water to cover the demand.


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Measure the turbidity (T.B. 2.13) and pH of each individual water source (T.B. 2.22) to determine the relevance of chlorination and the appropriate contact time. When the turbidity of the water to be treated is high, chlorination isn’t effective. The recommended turbidity value for efficient chlorination is set at 5 (N)TU, although turbidities up to 20 (N)TU are acceptable during the acute phase of an emergency. In case these values are exceeded, the amount of suspensible particles in the water has to be reduced by natural or assisted sedimentation (T.B. 2.16) and/or filtration (T.B. 2.17).


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Prepare a 1% chlorine solution (T.B. 2.20), preferably on a daily basis because correct storage conditions will most probably be lacking. Use non-metallic containers because metal consumes chlorine and will corrode rapidly.


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Carry out the chlorine jar test (modified Horrocks test; T.B. 2.21) for each individual water source.


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Determine the volume of the different water-collecting recipients from the beneficiaries. In case it proves to be difficult to estimate the volume of their recipients, a weighing scale can be used (1 kg = 1 litre of water).


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Inject with a syringe the appropriate amount of 1% mother solution, related to the volume of each individual recipient and based on the results of the modified Horrocks test.


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Do random tests on several containers to verify if a correct Free Residual Chlorine concentration (FRC) is reached:


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➞ if pH > 8, FRC of 0.4 - 1.0 mg/l after a minimum contact time of 60 minutes because chlorination is less effective if the pH is above 8.


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Insufficient FRC concentrations of the collected water can be due to dirty containers, thus resulting in a higher chlorine consumption (higher chlorine demand; T.B. 2.22).


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Keep chlorine-generating products in their original packaging which should be airtight, non-metallic or properly painted / enamelled containers. Shelter these products from heat, light and humidity, and store them in a restricted access area (chlorine is a dangerous product). Never store chlorine-generating products together with organic matter (e.g. food), nor with combustibles because of the risk of fire or explosion. For quantities larger than 10 kg, look for a separate storage place, away from equipment that could be damaged by corrosion (chlorine is a strong oxidant).


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It is recommended to provide to each chlorinator a table indicating the amount of 1% chlorine solution that needs to be injected per volume of recipient (based on the modified Horrocks test); e.g. 2ml of 1% chlorine solution for a recipient of 8 litres, 2.5 ml per 10 l, 3 ml per 12 l, 4 ml per 16 l, 5 ml per 20 l.


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The transport between the water point and a person’s home can be sufficient for both the mixing and the required contact time. Where this is not the case, a strategy will have to be implemented that insures the appropriate contact time.


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A distribution of clean recipients, in plastic material, such as jerrycans may be necessary to ensure that the population has proper and clean transportation and storage means. Moreover, as the recipients will all be of the same capacity, the chlorination will be easier. In case it isn’t possible to provide clean recipients, the cleaning of the beneficiaries’ containers should be envisaged.


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In situations where water is sold, it may be advisable that the water sellers are involved in the chlorination process, to ensure that the sold water is disinfected.


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Key users can be enabled to give feedback on water quality, if they are equipped with a pool tester (T.B. 2.22) and trained for checking the FRC concentration.


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Several products combining a coagulant, potentially some flocculants, and a disinfectant are available under the form of tablets or sachets. These products are intended for individual households or small scale (community) water treatment. A certain vigilance is required with these products because fixed doses of different chemicals are added to a determined amount of raw water that can have any quality, without performing a jar test (T.B. 2.15) or a Modified Horrocks test (T.B. 2.21). The Free Residual Chlorine concentration (T.B. 2.22) of the treated water should at least be analysed, and preferably also its residual aluminium or iron concentration (depending on the coagulant used in the product). In case any of the measured values are outside the normally used standards (indicators), advice should be sought from your technical referent. Besides the potential technical issues, a lot of attention should also go to the distribution procedure of these products. It is also important to


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In order to design a water supply system, it is necessary to conduct a survey identifying the topography of the proposed route. This will permit to calculate the characteristics of a water pipeline that will be gravity-fed or pressurised by a pump. The length is preferably measured by means of a long measuring tape, while the height difference can be calculated based on the length and the vertical angle in between the two extremities of the water supply system. The topographic surveys described hereafter are for simple and rather short water supply systems.T.B. 2.24 Basic topographic survey


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Determine by means of a long measuring tape (e.g. 50 m) the distance in between the two extremities of the water supply system, namely the water source and the utility point. If still needed, it should be verified if the proposed route will permit the excavation for a potential underground installation of the pipe.


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Stand at the lower extremity of the water supply system (e.g. river), hold the Abney level to the eye and sight the other extremity of the water supply system (e.g. reservoir) by centring the cross-hair against the target.


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Adjust the index arm until the bubble (visible in half of the field-of-view) is centred against the cross-hair and block the index arm with its fixing screw.


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Calculate the height difference in between the extremities of the water supply system by using the following formula:


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With H = height difference in between the extremities of the water supply system L = distance in between the two extremities of the water supply system


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α = angle between the horizontal level (measured at the eyesight of the surveyor standing at the lower extremity) and the upper extremity of the water supply system


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α = measured angle between the river and the outlet of the reservoir up the hill = 5° h = eyesight height of the surveyor = 1.71 m


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In this case, measurements must be taken from the bottom of the valley, first in the direction of one extremity


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(a) of the water supply system and secondly in the direction of the other extremity. The same procedure as described in A must then be followed twice. The height difference between the two extremities is then represented by the difference (ΔH) between H(a) and H(b).


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L(a) = distance in between the bottom of the valley and the extremity (a) (e.g. outlet of a reservoir) = 250 m


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α(b) = angle measured in between the bottom of the valley and extremity (b) = 7.8° h = eyesight height of the surveyor = 1.71 m


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Choose a reference point on a flat surface nearby the water tower from which all measurements will be taken.


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Determine the horizontal distance in between the reference point and the water tower by means of a measuring tape.


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Stand at the reference point, hold the Abney level to the eye and sight the highest part of the water tower by centring the cross-hair against the target.


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α = angle between the horizontal level (measured at the eyesight of the surveyor standing at the reference point) and the upper point of the water tower


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α = angle measured in between the reference point and the water tower = 24.5° h = eyesight height of the surveyor = 1.71 m


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Long complicated water supply systems passing several hills fall out of the scope of these guidelines (section 2.5 Further reading).


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All formules given are to be used with a calculator in the “degrees” mode. If the calculator is in “radians” mode, the angle should be converted in radians as well: degrees x π/180° = radians (π = 3,14).


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When making a topographic survey of a single slope for a gravity-fed system, the available height difference (pressure) to overcome the linear and local head losses (T.B. 2.31) should be measured in between the tap height and the outlet of the reservoir. This means that standing at the tap site, the outlet of the reservoir should be targeted with the Abney level. The height of the tap should be deducted from the calculated height based on the Abney level measurement (as described above).


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To determine the maximum pressure in a gravity-fed pipeline, the maximum height difference between the lowest point in the system and the maximum water level (in the reservoir) should be measured. This maximum height difference is important to verify the pressure the pipe has to resist to when all the taps are closed. When the maximum water level in the reservoir can’t be determined, its maximum height can be used as a reference.


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To be able to determine the pressure that a pump has to deliver pumping water uphill, the height difference should be measured in between the (dynamic) water level of the source and the maximum water level in the system (e.g. completely filled reservoir, highest point within the pipeline). To this pressure related to the height difference, the needed pressure to overcome the head losses (linear and local) should be added to determine the required pump capacity.


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In case the total height of a water tower has to be determined, the upper part of the reservoir should be sighted with the Abney level. However, in order to know the minimum pressure that the water tower will be able to provide, the lower part (outlet) of the reservoir should be sighted.


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The distance and the height difference can also be measured with a GPS, but be aware that the majority of these instruments only give an horizontal precision equal to 10 m and the vertical precision is even lower. So normal GPS systems aren’t that suited for topographic surveys.


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The clinometer is similar to the Abney level. It has a simpler concept and is cheaper, but as the sighting is more difficult to do, the precision is less accurate than with an Abney level.


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The altimeter functions by measuring the barometric pressure differences at different altitudes (lesser atmospheric pressure at higher altitude). As varying weather can change the barometric pressure as well, the measures should be taken in a short period. An alternative is to have one mobile and one or two fixed altimeters at the extremities of the topographic area under study. By measuring at regular intervals the pressure differences at the fixed altimeters, it will be possible to add a correcting factor to the measurements of the mobile altimeter. The altimeters precision of 1 to 5 m is often not sufficient.


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The theodolite and laser are both high-precision instruments that are expensive and might require special training. The accuracy obtained with these instruments (within centimetres) is usually not needed for topographic surveys.


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Most motorized (combustion engine or electric) water pumps used by aid-agencies are centrifugal types. The principle of a centrifugal pump is that its spinning impellor (rotor) throws the water outwards and the empty space that is created at the centre of the impellor is filled via the “suction pipe” by new water, which is actually pushed in by the atmospheric air pressure. This new water will be thrown outwards again by the impellor, creating again an empty space at its centre and so on continuously until the pump is stopped. The velocity of the water thrown out of the impeller is partly transformed within the pump’s snail house (stator with a specific form) into pressure, thus the water can be transported at a certain flow over a certain height.T.B. 2.25 Centrifugal pumps


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They will most of the time be situated above the water surface and will “suck up” the water to deliver it at higher grounds. Whatever the kind or the power of the motor driving the pump, its maximum suction height (head) is about 7 m at sea level, and decreases as the altitude rises.


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Low pressure motor pumps (e.g. maximum pressure of about 300 kPa or 3 bar), driven by a petrol or diesel engine, are often used in emergencies. As motor pumps are designed to work at construction sites, they can deal with very turbid water that contains small solid particles.


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Trash pumps (T.B. 3.13) are able to pump turbid water containing solids up to 20 – 30 mm (e.g. small debris, faeces) without clogging. Their impellor blades often have sharp edges to shred soft particles.


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They need to be completely submerged in the water, otherwise they stop or even break down after a short period of use. As they are completely submerged, these pumps don’t “suck up” the water, they only have to deliver (push) it. They are specifically interesting for (tube) wells that have their water level (a lot) deeper than 7 m under the surface. The flow and pressure that can be delivered, depend on the size of the pump and on the power of its electric motor (most often combined in one piece of equipment). Submersible pumps are designed to lift non-turbid water, thus solid particles in suspension will damage their impellers and pump house.


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They combine to a certain extent features of the commonly used motor pumps and the submersible pumps. Dewatering pumps that are driven by electric motors, can be completely submerged or nearly completely out of the water (as long as the impeller part stays submerged). Some high quality models exist that have their electric motor cooled by the pumped water, so the motor part can stay out of the water for prolonged periods. As their inlet has to be under the water level, dewatering pumps can only deliver water, but at (relatively) high flow rates. As these pumps are designed for (very) dirty water, their delivery height is rather limited (certainly in comparison to submersible pumps in the same electric power range). Aid-agencies use them mainly to dewater hand dug wells rapidly, before the works within can start. They can also be used during well cleaning (T.B. 2.03) or to remove the sludge from assisted sedimentation reservoirs (T.B. 2.16). They can also be employed to deliver potable


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works within can start. They can also be used during well cleaning (T.B. 2.03) or to remove the sludge from assisted sedimentation reservoirs (T.B. 2.16). They can also be employed to deliver potable water from hand dug wells that are more than 7 m deep.


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The maximum Total Manometric Head (TMH) it can reach (at zero flow); expressed in kPa, bar, meter Water Column (mWC).


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The maximum flow it can reach (theoretical working point at TMH zero); expressed in l/s, l/min, m³/h.


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pQ (upper part of the graph): The pQ curve of a centrifugal pump is the relationship between the pressure


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(p) and the flow (Q) it delivers (for a motor pump at the maximum regulated speed of the combustion engine). The curve determines the capacity of the pump over its working range. Note that at maximum pressure, the flow is zero. Often, a part of the curve is printed in bold. This is the range at which the pump should function to have a high efficiency. The actual working point (the specific pressure and flow at which the pump will function) is determined by the height difference and the head losses in the pipe system that the pump has to overcome (T.B. 2.31; 2.32).


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Pump efficiency and power requirements (lower part of the graph): Some manufacturers of (electric) centrifugal pumps also provide curves indicating the efficiency (Eta) and the power requirement (P2) of a specific pump. The efficiency is the relation between the power transmitted to the water and the power delivered by the motor. Every pump has its own efficiency curve, which will vary according its flow. The maximum efficiency is where most of the power of the motor is transferred to the water as shown on the curve. The power curve also shows that a centrifugal pump needs the least power when the flow is zero. So if a generator has difficulties to deliver the starting current of an electric centrifugal pump, it’s recommended to start it with its gate valve closed (Q = 0, p = max.), because this requires the least power, thus also the least starting current.


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Motor pumps and generators should never be lowered inside or put directly next to a well to avoid their toxic exhaust gasses accumulating within.


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Dewatering pumps should be stopped and disconnected from their electricity source before people enter the well.


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Not all surface centrifugal pumps are self-priming; thus not only their pump house has to be filled completely with water before the pump is started, but also their “suction” pipe. In case of doubt if a pump is self-priming, always fill its “suction” pipe with water.


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Some high capacity surface pumps can’t “suck up” the water and need to have the water level at the same height as the pump axis, or even above (check the owner’s manual).


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Not all centrifugal pumps are capable of pumping turbid water. The possible presence of large quantities of sand or other solid particles in the water may damage the moving parts of the pump.


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The installation of a strainer is compulsory, even for pumps which are specifically manufactured to deal with water that contains solid particles.


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Some electric pumps have electronic features that start their motor slowly and thus require a lower starting current (consequently also less starting power). It is therefore not necessary to start this kind of pumps with a closed gate valve.


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Be aware that 10 meter Water Column (mWC) is about equal to 100 kPa or 1 bar (with bar and mWC being the unities most commonly used by technicians).


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➞ and the time available to fill the reservoirs, which is depending on the moment of the day when the population is collecting the water (mainly in the morning and early evening) and/or on the space of time


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Collect physical information related to the site: check the diameter and the depth of the hand dug well or borehole, make a sketch with the dimensions of the river bank, the water’s edge of the lake or canal (for the determination of the place availability to install a pumping station), verify the altitude (height above the sea level).


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Determine if the yield of the water source can cope with the desired pump flow. If information on the maximum yield of a (tube) well is not available, a pumping test should be performed (T.B. 2.27).


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Specify the purpose of the pump: e.g. the pump will be used for water treatment using chemicals as aluminium sulphate or ferric chloride.


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Determine the exact locations of the water source, the pumping station and the reservoirs, and make a topographic plan that:


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➞ indicates the vertical distance in meters between the lowest water level and the highest level to which the


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water has to be pumped, or in other words the Total Geometric Head (TGH) (T.B. 2.24). Note that the highest point is not necessarily the storage reservoir. Take also the possible seasonal variations of the water source levels into consideration.


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➞ gives the total length of the pipe in order to calculate the Total Head Losses (THL). The head losses include the linear head losses (friction of the water passing through the pipe) and the local head losses


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<table><tr><td>Total Manometric Head (TMH): total pressure the pump has to deliver (expressed in mWC, kPa or bar) Total Manometric Head (TMH) = Total Geometric Head (TGH) + Total Head Losses (THL) Total Geometric Head (TGH) = Geometric Suction Head (GSH) + Geometric Delivery Head (GDH) Geometric Suction Head (GSH): from the water resource level to the centre (axle) / inlet of the pump. Remark: Be aware that for (tube) wells the dynamic water level at the desired flow should be used. Geometric Delivery Head (GDH): from the pump axle / impellors to the highest point in the delivery system. Remark: Once the water is pumped over the highest point in the delivery system, siphoning can occur if the actual outlet is at a lower level, which will reduce the Geometric Delivery Head. Still, it is recommended to use the initial GDH to determine the pump in order to be sure that the system will work (assuring that the pump is capable of pushing the water over the highest point). The final result can then only be that the obtained flow is somewhat higher than initially expected. Total Head Losses (THL) = Suction Head Losses (SHL) + Delivery Head losses (DHL)</td></tr></table>


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Total Manometric Head (TMH): total pressure the pump has to deliver (expressed in mWC, kPa or bar) Total Manometric Head (TMH) = Total Geometric Head (TGH) + Total Head Losses (THL) Total Geometric Head (TGH) = Geometric Suction Head (GSH) + Geometric Delivery Head (GDH) Geometric Suction Head (GSH): from the water resource level to the centre (axle) / inlet of the pump. Remark: Be aware that for (tube) wells the dynamic water level at the desired flow should be used. Geometric Delivery Head (GDH): from the pump axle / impellors to the highest point in the delivery system. Remark: Once the water is pumped over the highest point in the delivery system, siphoning can occur if the actual outlet is at a lower level, which will reduce the Geometric Delivery Head. Still, it is recommended to use the initial GDH to determine the pump in order to be sure that the system will work (assuring that the pump is capable of pushing the water over the highest point). The final result can then only be


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the initial GDH to determine the pump in order to be sure that the system will work (assuring that the pump is capable of pushing the water over the highest point). The final result can then only be that the obtained flow is somewhat higher than initially expected. Total Head Losses (THL) = Suction Head Losses (SHL) + Delivery Head losses (DHL)


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The ease of maintenance and the robustness of the pump; the number of hours the pump has to run or the number of times it has to start per hour; the availability of fuel (what type of fuel) or electricity; the availability of tools, spare parts and maintenance skills; the purchase, running, maintenance and repair costs; these are all factors that should not be underestimated in the choice of a pump (and certainly not for long-term use).


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Electric motors require a higher current (thus more power) to start than to run normally. This should be taken into consideration for the choice of a generator. The required starting current can be reduced for a centrifugal pump by starting it with a closed gate valve at the delivery side. However, this valve has to be opened as soon as the pump has reached its normal regime (only some seconds). Some electric pumps have electronic features that start their motor slowly and thus require a lower starting current (consequently also less starting power). It is therefore not necessary to start this kind of pumps with a closed gate valve.


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Water hammering is a phenomenon that happens when water flowing in a pipe is suddenly stopped (e.g. by quickly closing a ball or a butterfly valve), which results in pressure building up rapidly and the water shooting back in the opposite direction. This leads to several (high) pressure peaks (hammering), and which can end in a damaged water supply system. Only gate valves should be used in pumping systems because their closing time is slow, thus the risk of water hammering reduces drastically (ball and butterfly valves should not be used).


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The suction ability of a surface pump is limited to maximum 7 m at sea level, whatever its motor power. Therefore should the suction height (head) be as small as possible and the length of the suction pipe as short as possible. The suction ability diminishes as the altitude increases (see table hereunder).


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<table><tr><td>Altitude (m)</td><td>Loss of suction head (m)</td></tr><tr><td>0</td><td>0</td></tr><tr><td>500</td><td>0.60</td></tr><tr><td>1000</td><td>1.20</td></tr><tr><td>1500</td><td>1.70</td></tr><tr><td>2000</td><td>2.20</td></tr><tr><td>2500</td><td>2.70</td></tr><tr><td>3000</td><td>3.20</td></tr><tr><td>3500</td><td>3.60</td></tr></table>


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Altitude (m) Loss of suction head (m) 0 0 500 0.60 1000 1.20 1500 1.70 2000 2.20 2500 2.70 3000 3.20 3500 3.60


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Motor pumps should never be lowered inside or put directly next to a well to reduce the length of the suction pipe.


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Not all surface centrifugal pumps are self-priming, thus not only their pump house has to be filled completely with water before the pump is started, but also their “suction” pipe. In case of doubt if the pump is self-priming, always fill the suction pipe with water.


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Some high capacity surface pumps can’t even “suck up” the water and need to have the water level at the same height as the pump axis, or even above (check the owner’s manual). They can only deliver water up to a certain height at a certain flow, which depends on the power and the rotation speed of the motor.


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The presence of salty or brackish water may require a special pump that is less vulnerable to corrosion.


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The height of the water column in a well creates a pressure at the entrance of the submerged pump, thus the Geometric Suction Head (GSH) is negative and needs to be subtracted from the Geometric Delivery Head. This means in practice for submersible and de-watering pumps that the Total Geometric Head can be counted from the dynamic water level until the highest point in the pipe system. Be aware however that some pumps have a maximum pressure (depth) to which they can be submitted. Take also into account that the deeper the pump is lowered inside a well, the longer the delivery pipe has to become, thus the higher the delivery head losses will be.


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The suction head losses for submersible and de-watering pumps are very low because there aren’t any inlet pipes causing friction. However, the friction of the water with the gravel pack and slotted casing of a borehole cannot be neglected (T.B. 2.27).


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Check the well’s logbook for following information: total depth, static water level, dynamic water level at maximum pumping rate and depth where the slotted part of the tube well starts. If the logbook isn’t available, all the above mentioned data have to be determined before a pump can be chosen and/or installed. Information on neighbouring wells can provide an estimation of the well depth and the static water level in the area.


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Determine the total depth of the well. This can be done by introducing a disinfected heavy weight (e.g. a stone) on a long rope into the well. Once the weight can’t be felt anymore, the bottom is reached. The length of the inserted rope, starting from the ground surface (e.g. the edge of the wellhead / the casing aboveground) until the bottom can be measured, and therefore indicates the total depth of the well.


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Determine the static water level of the well by means of a dipper. A dipper is a probe connected to a long measuring tape that will give a light and/or sound signal when it comes in contact with water. To obtain correct data, the static water level measurement should only be done when the well hasn’t been used for at least 24 hours.


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Estimate, in case of a borehole, the depth where the slotted casing starts, based on its total depth and the static water level. A properly designed borehole often has 1 to 3 lengths of slotted casing of 4 to 6 m length each, depending on the extent (thickness) of the underground aquifer. It’s important to consider that a correctly designed borehole can never have its static water level lower than the slotted part of the casing.


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Install a motorized centrifugal pump (T.B. 2.25). For shallow wells (static water level less than 6 m deep at sea level), a motor pump can be used. For hand dug wells with a deeper static water level, a dewatering or a submersible pump will have to be used. For deep tube wells a submersible pump will need to be installed, at least 1 m above the slotted casing (T.B. 2.29). A gate valve should be foreseen on the delivery pipe to regulate the pump’s flow accurately.


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Start the pump with the gate valve closed, open it slowly and regulate the flow “Q” at 0.5 m³/h by means of the valve. The flow can be determined by measuring the time needed to fill a recipient of known volume (e.g. 20 - 30 l), or a lot easier by an instant flow meter.


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Measure the drawdown “s” (in meter) with the dipper, and follow up until the dynamic water level has stabilized (drawdown < 1 cm/minute) at this specific flow rate. Often a stabilization period of 2 hours is taken, but in acute emergencies,it can be tried to reduce this period.


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Plot the measured figures on a flow (abscissa) / drawdown (ordinate) graph to indicate the working point. A straight line can also be drawn from the graphs zero point (flow = 0, drawdown = 0) across the first flow (Q = 0.5 m³/h) / drawdown (s) working point, representing more or less the linear head losses within the aquifer (as the non-linear head losses will mostly still be low for such a low flow).


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Measure also the turbidity of the well water by means of a turbidity tube (T.B. 2.13). The turbidity should preferably be less than 5 (N)TU, and certainly not above 20 (N)TU.


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Increase the flow to 1 m³/h by opening the gate valve a little more, and whilst monitoring the turbidity. follow the drawdown over the same period as for the flow of 0.5 m³/h.


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Plot the new working point on the graph and interconnect the different working points to form the well curve, representing the linear and non-linear head losses during pumping (as per figure C).


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Keep adding a step of 1 m³/h to the flow rate while measuring the drawdown, and keep on plotting the results on the graph, until the non-linear head losses have become equal to the linear head losses, or until the well curve bends significantly away from the linear head losses line. These phenomena indicate that the critical flow is reached. The critical flow is also reached when the turbidity of the pumped up water starts to rise drastically. In case these phenomena don’t occur, the flow rate can be increased until the maximum possible drawdown is reached, meaning that the dynamic water level is still at least 1 m above the pump (or the strainer if a surface pump is used).


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When a well is being over-pumped beyond its critical flow, it can result in the well curve bending significantly away from the linear head losses line. This is caused by:


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➞ important turbulence and thus heavy non-linear head losses within the gravel pack and the slotted casing


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In any case, over-pumping should be avoided. This means that the maximum pumping rate should be below the critical flow. In practice, and to play on the safe side, the pump flow rate of the last step before the critical flow is reached, can be considered as the practical maximum pumping rate.


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A serious increase of the turbidity also indicates that the (tube) well is over-pumped. The maximum pumping rate should then be regulated at the flow delivering water with a turbidity of less than 5 (N)TU (maximum 20 (N)TU during acute emergencies).


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In case the critical flow isn’t reached, nor the turbidity has risen, the maximum pumping rate should be set at the flow at which the dynamic water level in the well is at least 1 m above the pump / strainer.


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Based on all the results, a logbook with all the available information should be made and archived for future use.


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This simplified pumping test provides the possibility to determine rapidly an approximation of the most essential parameters that are needed to exploit safely an existing well. However, the approximations made above do not guarantee any long-term results for the tested well. Other more sophisticated methods exist (e.g. Porchet) and can be found in specific literature (section 2.5 Further reading).


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➞ Total depth: in practice the depth from the edge of the wellhead or from the casing aboveground, until the bottom of the well.


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➞ Static water level: water level before pumping starts (not having been pumped for at least 24 hours).


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➞ Dynamic water level: water level at a certain pumping rate, preferably at the well’s maximum pumping rate (but certainly not above).


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➞ Maximum pumping rate: the maximum water flow that the well can deliver without having important non-linear head losses, too high turbidity of the water or being sucked dry.


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Even if the logbook of the well is available, it can be interesting to verify all its data, at least if time permits.


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When determining the total depth of the (tube) well, make sure there aren’t any obstacles blocking the free passage of the weight and rope (e.g. a pump).


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An appropriate submersible pump should be installed with its bottom at least 1 m above the slotted casing of the tube well, in order to avoid:


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A dewatering pump or the strainer of a motor pump’s “suction” pipe should never be less than 0.5 m away from the bottom of a hand dug well. This is to avoid that settled dirt particles would be pumped up, which would increase the turbidity drastically from the start.


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If the turbidity of the well water is already high before the pumping test starts, it can be an indicator that the well hasn’t been designed correctly (e.g. no lining for a hand dug well) and/or developed properly (no slow pumping during prolonged periods). Another possibility is that the well has been over-pumped previously.


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Where water is scarce, avoid wastage during the pumping test by collecting the water in a reservoir.


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The distance in between the well curve and the linear head losses line indicates the non-linear head losses, created by the turbulent flow inside the gravel pack and the slotted casing of the tube well.


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If time is available, it is preferable to increase the flow in steps of 0.5 m³/h, instead of 1 m³/h.


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It is also possible to do a pumping test with a flow in between the two measures where the critical flow appeared, in order to determine the maximum pumping rate more precisely. This is recommended if the “initially obtained” maximum pumping rate is too low in comparison with the desired flow (and thus not covering the water demand).


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After the maximum pumping rate has been determined, it’s recommended to pump at this rate for 24 hours, in order to verify the capacity and the stability of the well.


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Choose the pumping site: it should be easily accessible in all seasons and not liable to flooding, particularly where the pump is to be used for filling water trucks.


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Prepare the site so as to install the pump as close to the source as possible, in order to reduce the suction head, but keeping in mind the potential sudden water level differences. Motor pumps should never be lowered inside or put directly next to a well, to avoid their toxic exhaust gasses accumulating within.


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Fit the strainer with foot valve at the lower end of the suction pipe. Attach a float so as to hold the strainer about 0.3 m below the water surface to avoid creating eddies and thus sucking in air and/or floating vegetation, and preferably 0.5 m (at least 0.3 m) above the bottom to avoid sucking in mud.


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Lay the suction pipe on a rising slope (avoid dips if possible), making sure that all the connections are well tightened. An air leak through the connections or a hole in the suction pipe could mean losing the priming of the pump. The total suction head should be limited to 7 m (at sea level). If possible, restrain to one suction pipe as this limits the risk of air leaks and reduces the suction head due to friction losses.


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Lay the delivery pipe up the slope towards the reservoir / tanker filling point and make the connections.


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Check always the oil level of the pump engine before starting. Be aware that new motor pumps are most often delivered without oil in the engine.


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Fill up with fuel. For safety reasons, refuelling should only be done when the engine has cooled down.


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Check regularly the general condition of the motor pump (e.g. the air filter, the spark plug), according to the manufacturer’s instructions.


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Fill the pump body with water. Most motor pumps provided under kit form are self-priming, so filling the suction pipe to encourage priming isn’t essential. However, for some (high pressure) pumps and older self-priming pumps, and/or when the suction head is high (e.g. nearly 7 m at sea level), it is required to prime the suction pipe as well. In case of doubt, it is always best to fill the suction pipe.


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Start up the pump, following the instructions of the user’s manual. Make sure to know how to stop the pump before starting it, to be ready in case something would go wrong.


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Record the pumping periods in the maintenance book to keep a count of the hours the pump has been running, and to plan the engine’s maintenance schedule.


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Verify the borehole’s static water level, the level where the slotted casing starts, its maximum pumping rate and the corresponding dynamic water level. This can be verified by looking in the borehole’s logbook and/or by doing a pumping test (T.B. 2.27).


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Choose a submersible pump corresponding to the water demand, the amount of time the pump has to run, the electricity supply, the delivery height of the water, while keeping in mind the maximum pumping rate of the borehole (T.B. 2.26).


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Verify if the wellhead is complete with an elbow, a gate valve and a (fast-)coupling on the outside, and a hook for the security rope on the inside. It should also have a closable opening to introduce a dipper (T.B. 2.27), and a “sealable” opening for the electrical power cable.


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Lay the submersible pump next to the existing borehole on a piece of plastic sheeting and roll off its electrical power cable in a straight line.


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Roll off the raising main next to the electrical power cable, starting from the pump side. The raising main can be a special flat hose or a PE pipe, as long as it has the correct diameter.


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Cut the raising main to the correct length; the pump should be at least 1 m under the dynamic water level at maximum pumping rate, and at least 1 m above the slotted part of the casing. When determining the raising main’s length, keep in mind that there might be variations in the water level according to the seasons. As the pump should be hanging directly on the pipe, be also aware that the raising main itself might stretch for up to 3% once it’s filled with water.


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Connect the raising main couplings tightly with Teflon tape to the submersible pump on one side, and to the wellhead on the opposite side.


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Put short lengths of PVC or PE pipe around the electrical power cable at the level of the couplings to avoid it getting damaged by friction.


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Fit the electrical power cable with the provided cable straps (or PVC tape) to (the loops of) the raising main, allowing a little slack (5% by snaking the cable). The electrical power cable should be fixed at every meter of raising main.


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Pass the power cable through the foreseen hole in the wellhead before installing the electrical plug.


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Lay out a rope next to the raising main and electrical power cable. A polypropylene (PP) rope with a minimum diameter of 5 mm is recommended for use in boreholes because it won’t rot in this humid environment.


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Cut the rope to the correct length. As the pump won’t be hanging on this rope (it’s only there as a security in case something would go wrong), it has to be at least 3% longer than the raising main in order for the latter not to kink which would cause serious local head losses; e.g. for 50 m of pipe, the rope should be at least 51.5 m.


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Make sure that the aboveground edge of the casing is cut horizontally because it will be the support of the wellhead.


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Lower the pump with its raising main, cable and rope into the casing whilst cleaning them with water and a cloth soaked in a 0.05% chlorine solution. Take care not to damage any of them. Be aware that the weight will accumulate as the pump with its electrical power cable and the raising main (e.g. 0.5 kg/m) is lowered deeper and deeper in the casing.


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Verify the drawdown when pumping for the first time to avoid that the pump would run dry, and check the turbidity (T.B. 2.13) of the pumped up water (a higher turbidity could indicate that there is over-pumping of the borehole). Adjust the pump’s yield with the wellhead’s gate valve, if necessary.


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The relatively easy installation procedures described here are only valid for submersible pumps that have all their protection facilities (e.g. dry run, over- and under voltage, overloading) integrated in the pump itself, thus not needing an external control panel.


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Submersible pumps should preferably be ordered with the electrical power cable already installed, because a faulty installation (e.g. leakages in the electrical isolation) can lead to serious damages and electrocution if a metallic raising main would be used.


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Some aid-agencies provide submersible pumps with all the needed accessories under kit form in order to equip existing boreholes rapidly during acute emergencies. These pumps can be powered with portable generators. Although it is tried to cover a wide flow range, the available variety of submersible pumps in these emergency kits is limited. So for chronic emergencies and stabilized situations, it is strongly recommended to purchase submersible pumps with their accessories (e.g. rising main, wellhead, rope), fully adapted to the delivery height, the desired flow and the corresponding head losses. Remember that the desired flow should not be above the maximum pumping rate of the borehole.


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It is possible to install a small submersible pump with a limited length of flexible raising main manually, but the weight, accumulating as the system is lowered deeper and deeper in the borehole, should not be underestimated. In any case, a minimum of two persons should be located directly at the borehole to lower the pump inside the casing, without the cleaned and disinfected raising main, electrical power cable or rope dragging over its edge. At least a third person should bring the wellhead closer to the borehole as the pump, raising main, electrical power cable and rope are lowered. Other options are to lower the submersible pump and its accessories by means of a rolling wheel (and a car), or a tripod.


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The pump should be lowered or hoisted by the pipe, and the rope and electrical power cable guided. Never pull on the electrical power cable.


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Although often used as raising main, metal pipes are rigid and heavy, and thus more difficult to transport, to install and to retrieve. For the installation and retrieval of such a pump system (e.g. for maintenance or repair purposes), a tripod with pulley-block will be needed. These pipes are also vulnerable to corrosion (at their connections), even if they are made of galvanised iron or epoxy coated steel. Nevertheless, their availability on the spot can be higher than for other materials and they allow the construction of very solid systems.


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Once the submersible pump is installed in the borehole, it’s recommended to verify its correct functioning and if its yield doesn’t exceed the maximum pumping rate of the tube well. This can be verified trough a pumping test (T.B. 2 27), with the help of an instant flow meter and a special device to measure the water level, often called a dipper. In case the maximum pumping rate would be exceeded, the flow of the pump can be reduced by closing the gate valve on top of the wellhead a little.


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For installation in a hand dug well, the submersible pump often needs to be positioned horizontally to stay 1 m under the water surface (dynamic water level) and at least 0.5 m above the bottom of the well. These distances should be respected to avoid the submersible pump respectively going too often into dry-run protection, or “sucking up“ settled particles. To avoid suspensible particles to settle on the horizontally positioned pump and therefore reducing its cooling, it needs to be installed within a cooling mantle that is hanging on ropes or standing on long legs.


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Electrical dewatering pumps can also be used within hand dug wells to retrieve potable water, just by being hung up at least 0.5 m above the bottom of the well (similar to figure B in T.B. 2.03). However, attention should be paid not to over-pump the well because dewatering pumps can have a big yield.


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During the first step of hand dug well cleaning, a dewatering pump can be put on the bottom of the well to remove as much sludge as possible (these pumps are capable of dealing with reasonable amounts of turbid water). Afterwards, the pump should be hung at least 0.5 m above the bottom of the well to dewater the hyper-chlorinated water of the disinfection process (T.B. 2.03). During human activities inside the well, the dewatering pump should be stopped and disconnected from the electricity supply to avoid electrocution.


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Lay-flat hoses (fireman’s hoses) are commonly available in emergency kits in rolls of up to 50 m and diameters of 2 or 3” (Nominal Diameter ND 50 or ND 80). Being collapsible when not in use, lay-flat hoses can be rolled up in relatively small volumes, which eases their transportation. However, lay-flat hoses cannot be used at the suction side of a pump, they cannot be buried as such in the ground and they tend to kink when changing direction, causing a lot of local head losses (T.B. 2.31). The connections to pumps, tanks or to each other are often made with fast couplings. They usually have a pressure resistance equal or higher than spiralled pipes.


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Spiralled pipes (Heliflex pipes) can be used at the suction and the delivery sides of a pump. Spiralled pipes that are usually found in emergency kits have a diameter of 2 or 3“; (ND 50 or ND 80). They usually have a pressure resistance of up to 6 bar. Because they are flexible, some coils of spiralled pipes are often delivered with emergency water tanks and pump kits, permitting the rapid installation of short pipelines. Because of the used couplings and the corresponding high local head losses, Heliflex pipes are often only installed on short distances. Due to their spiral reinforcement, these pipes can also be buried.


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Especially the smaller diameter PE pipes are flexible. At diameters of up to 75 mm, PE pipes are often sold in coils of tens of meters. PE pipes are easy and fast to install, which explains why they are more and more used in emergencies. The common method for joining PE pipes is through welding, but mechanical couplings are often used as well for small diameter pipes. There are several commercial welding techniques available, from which butt and electro fusion are probably the most common. Both techniques will require a generator. The butt fusion technique uses a welding machine that melts both pipe butts, usually by a hot plate, and then pushes them together to form a watertight joint. The electro fusion technique is probably more easy to use, especially for repairs. It involves a sleeve into which the two pipe ends slide and fuse together once the fitting is connected to the generator. Fusion indicators are commonly designed into the fittings. When sufficient melt pressure has been


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into which the two pipe ends slide and fuse together once the fitting is connected to the generator. Fusion indicators are commonly designed into the fittings. When sufficient melt pressure has been generated, the indicator will protrude. A welding machine is only worth obtaining if several kilometres of PE pipes have to be installed. Although it is strongly recommended to bury PE pipes, they have already been installed aboveground for relatively long periods during emergencies.


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PVC pipes are far less flexible than PE pipes. PVC pipes are commonly available in lengths of 4 to 6 m with push fit insertion joints (collars) or joints that require solvent cement (PVC glue). After both pipe ends have been degreased, the PVC glue can be applied in a longitudinal way on both joints to form a watertight seal once the pipes are pushed into each other. Both glue and degreaser are IATA regulated and cannot be air transported without special authorisations and precautions. Note that not all PVC glue can resist the high pressures that are sometimes reached in potable water supply systems. This should be taken into account when this product is bought locally. PVC pipes should always be protected against direct sunlight.


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Galvanised iron pipes are commonly available in lengths of 4 to 6 m and diameters of up to 4” (100 mm). It is advised to use GI pipes only in special occasions because they are heavy and often expensive. GI pipes can be used for area’s where the pipeline:


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GI pipes are screwed together through a socket or unions. When sockets are used, one has to make the joint watertight by wrapping PTFE (Teflon) tape or hemp with paste around the thread in a clockwise direction before screwing the pipe together. In most countries, pipe-threading sets can be found on the local market (feasible to thread diameters up to 1.5” manually).


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To choose the right pipe type, one has to take several factors into consideration such as; the context (emergency or stabilized situation), the volume for storage and transport purposes, the local availability, the quality, the purchase and transport costs, the soil or environmental conditions, the nominal pressure that might occur in the pipes, the easiness to install and to dismantle, the head losses (T.B. 2.31), the available diameters. For long-term systems, it can be worthwhile to test the quality of plastic pipes (PE and PVC). Contact your technical referent if you want to have a test done in Europe to verify if the plastic pipe complies with the standards for food quality, pressure resistance and aging.


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All pipes do have a pressure rating, often expressed in PN (Pression Nominale / Nominal Pressure). The maximum nominal pressure should normally be mentioned on the plastic pipes. A rating PN 6 means that the pipe can resist a nominal pressure of up to 6 bar, and should not be exposed to higher pressures as it risks to burst (certainly over time). The pressures will need to be calculated in order to choose the right kind of pipe (T.B. 2.31; 2.32).


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The sizes of PE and PVC pipes are specified in terms of nominal outside diameter (OD), not by the internal diameter. The inner diameter of plastic pipes depends on the nominal pressure they can sustain: the higher the pressure, the thicker the pipe wall, the smaller the inner diameter. Typical pressure ratings for plastic pipes are PN 4, PN 6, PN 10 and PN 16. In case pressures above 16 bar can occur inside the pipe, other materials like GI will be required.


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To cover longer distances in (acute) emergencies, lay-flat hoses or sometimes PE pipes are installed aboveground because they exist in rolls of tens of meters, which reduces the installation time drastically. In a later stage with correct underground installation (T.B. 2.33), PE is the preferred option over PVC, although they are often more expensive to purchase. PE pipes are faster and easier to install and when there is a rupture of the tube, it will stay localised, whereas a PVC pipe can burst over its entire length.


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In order to keep the pipes safe from damages or deformation, it is important to store, handle and transport them with care.


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➞ Pipes should never be stored in a pile higher than 1.5 m, in order to avoid accidents and/or damages to the


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➞ PVC pipes with push fit insertion joints (collars) should be stacked in an alternating manner to avoid deformation of the tubes and they must also be stored on a flat surface.


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➞ In case the pipes are exposed to sunlight, they should be covered completely. Plastic will become brittle over time, even when they have been treated to resist UV-radiation.


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➞ In cold temperatures, plastic pipes get more brittle and therefore break easier. Specific precaution is needed during handling and transport.


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➞ Contact with hard surfaces like stones, concrete or metal could damage the plastic and even the threads of GI pipe. It is therefore also important to carry the pipes, and not to drag them along, nor to drop them on the


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Besides the PVC pipes for potable water supply, there are also PVC pipes for rainwater and wastewater drainage. The drainage pipes are not capable to withstand the pressures that are often obtained in potable water supply systems, thus they should never be used for that purpose. On top of that, their plastic often doesn’t comply with food quality standards.


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An alternative to welding machines is to weld PE pipes together manually. A metal plate is heated by means of a gas or kerosene torch, to which both PE pipe butts are melted before being pushed manually against each other. The right welding temperature of the metal plate can be verified by means of heat indicating crayons.


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If a lay-flat hose is put horizontally along a slope, the hose might roll towards the bottom of the slope once it is filled. This can be avoided by putting the hose in a shallow (open) trench. If a lay-flat hose is put vertically on a slope, the filled hose might snake into a zigzag shape.


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Special lay-flat hoses exist to install submersible pumps into boreholes (T.B. 2.29). Their extreme high tension strength and special couplings resist the heavy weight of the water column and pump hanging directly on the hose. Such an installation should never be made with the normal fireman’s hoses that can be found in the emergency kits.


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The local head losses, caused by the friction of water passing through accessories such as valves (even when completely open), bends, Tee-pieces, connections.


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The head losses are most often expressed in meter Water Column (mWC) per 100 m of pipe length or percentage; a head loss of 1% corresponds to 1 mWC (0.1 bar) per 100 m of pipe length.


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The linear head losses (ΔH) depend on several factors (represented on the nomograph), which are all interrelated:


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The velocity (v) of the water within the pipe (m/s): it depends on the flow and the inner pipe diameter.


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For a constant flow, same length and roughness of the pipe, the smaller the diameter, the higher the velocity in the pipe and thus the higher the head losses will be (as per figure A).


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For a same diameter, length and roughness of the pipe, the more the flow increases, the higher the velocity in the pipe and thus the higher the head losses will be (as per figure A).


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For a constant flow, same diameter and length, the rougher the pipe, the higher the head losses will be.


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For a constant flow, same diameter and roughness, the longer the pipe, the higher the accumulated head losses will be.


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When the information of two factors is known, their figures can be plotted on their respective column on the nomograph. By connecting these plotted figures by a straight line over the whole width of the nomograph, the other factors can be directly read or simply calculated.


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If the inner diameter of the pipe and the desired flow are known, the velocity of the water in the pipe and the linear head losses per 100 m pipe length (depending on the material of the pipe) can directly be read. To know the real linear head losses, its figure just has to be multiplied by the real pipe length (taking into account the multiplying factor 100).


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If the maximal potential linear head losses are calculated (depending on the available height difference; T.B. 2.24) and the inner pipe diameter is known, it’s possible to read the maximal potential flow passing through the pipe (taking into account the complete pipe length).


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If the desired flow is known and the maximal potential linear head losses are calculated, it’s possible to read immediately the needed minimum inner pipe diameter.


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To calculate the local head losses, tables exist which indicate for all kinds of accessories the frictional head loss factor to be used in the calculations. However, for simple pipelines with a reasonable length (e.g. some hundreds of meters) and few accessories, the local head losses are often estimated as 15 % of the linear head losses. This estimation isn’t valid of course for (rather) complicated pipelines and networks; for instance inside buildings where there are a lot of bends, valves and T-pieces. In case of doubt, contact your technical referent for more information.


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➞ Inner pipe diameter: its choice is restricted by the limited availability of different pipe diameters.


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The diameter mentioned on the nomograph is the inner diameter. Take this certainly into account for plastic pipes because their outer diameter is standardised in size, whilst their resistance to pressure depends on their wall thickness, and therefore has an influence on their inner diameter. For instance, the inner diameter of a PN 16 pipe is smaller than the inner diameter of a PN 6 pipe of the same external diameter (T.B. 2.30).


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➞ A velocity less than 0.7 m/s might result in particles settling inside the pipe, eventually clogging it.


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➞ A velocity higher than 3.0 m/s might result in particles eroding the pipe, and the risk of serious water hammering increases (T.B. 2.26).


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For a gravity flow system, the total head losses, expressed in mWC, can never be higher than the height difference in between the water source and the outlet.


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Similar head losses are present when water is moved upwards by means of a pump. When a pump is to be chosen (T.B. 2.25; 2.26; 2.28), these head losses expressed in mWC have to be added to the real height difference that the pump has to overcome (initially the height in between the water surface and the highest point in the water system).


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It is very difficult, if not impossible to estimate the head losses for Heliflex pipes and lay-flat hoses. Some Heliflex pipes have a high “roughness” due to the spiral that is also noticeable on its inside. When several Heliflex pipes are connected to each other, their double fast-couplings, present every so many meters (e.g. 6 - 8 m), will create a lot of local head losses as well. Lay-flat hoses might be quite rough on the inside as well, and they kink very easily (already at the slightest change of direction), thus creating a lot of unpredictable local head losses.


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➞ Determine the height difference between the outlet of the spring / reservoir and the end tap(stand) / valve (indicated as H2 in the figure).


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➞ Determine the maximum pressure that potentially will be applied on the pipes. This maximum pressure is exercised at the lowest point of the gravity flow system when the water isn’t moving (all taps / valves closed).


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Be aware that the lowest point of the system does not necessarily mean the end tap / valve. Thus the maximum pressure in the system is determined by the height difference in between the outlet of the spring or the highest water level in the reservoir and the lowest point of the pipeline (indicated as H1 in the figure). So the maximum pressure in the pipeline is expressed in meter Water Column (mWC), or bar (if divided by 10).


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Shortlist amongst all the available pipes the types that will resist the maximum pressure (e.g. PE, PVC, GI; T.B. 2.31).


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Choose a specific pipe within this shortlist, and measure its inner diameter (mm). The choice should be based on aspects like costs, availability, transport problems, roughness, food grade quality.


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Determine the flow that needs to pass through the pipeline (converted into l/s), depending on the amount of water (water demand) that needs to be transported over a desired or available time frame.


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Plot both the inner diameter and the flow figures on the nomograph (T.B. 2.30). It’s recommended to do this on a copy of the nomograph.


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Interconnect both plotted points with a ruler and draw the line over the whole width of the nomograph.


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Read the head loss in mWC per 100 m of pipe length, depending on the pipe’s material (related to the roughness of PVC / PE or GI).


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Calculate the total linear head losses according to the total length of the pipe and add the estimated 15% of local head losses to obtain finally the total head losses in mWC.


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Compare the total head losses in mWC with the total available pressure at the outlet (height difference H2 in between the water outlet of the spring / reservoir and the tap / valve). When the total head losses are deducted


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from the total available pressure, there still should be a positive pressure to overcome the local head losses of the tap / valve (minimum 1.2 m and up to 7 m for some tap models).


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Restart the exercise using a decreased flow and/or an increased pipe diameter in case the above mentioned positive pressure isn’t reached (or even be negative). The exercise on the determination of the head losses will have to be repeated until an acceptable result is found.


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The design of this simple gravity flow water supply system has its reservoir centralised nearby the source, but the distribution takes place at a certain distance. The shortest distance between both is through a small valley. The water demand can be satisfied with one tapstand.


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PN 6 pipe (max. 6 bar or 60 m pressure) will withstand the maximum pressure (35 m height or 3.5 bar) at the bottom of the system when all the taps are closed, so it can be used.


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➞ The nomograph indicates a head loss of about 1 mWC per 100 m pipe length and the velocity is just at the limit to avoid sedimentation in the pipe (0.7 m/s).


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➞ 6m available pressure - 4.6 m head losses = 1.4 m pressure left over to overcome the tap head losses.


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Conclusion: the system will work, but at a slightly lower flow than was expected (about 10 l/min per tap). The velocity in the pipe will also drop below 0.7 m, thus there is a risk of sedimentation within the tube. In case the wanted flow of 1.35 l/s is essential, the simplest solution would be to lower the tapstand by minimum 0.2 m (if the recipients of the beneficiaries would still fit underneath).


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H1: height difference in between the highest level in the reservoir and the lowest point in the valley H2: Height difference in between the outlet of the reservoir and the taps


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The above mentioned maximum pressure in the pipe is not considering potential water hammering (T.B. 2.26), which is caused when the water flow is suddenly stopped by closing a ball valve for instance or by an accidental immediate blockage of the pipe. Water hammering, which are enormous pressure shocks, can cause serious damages to the system and even personal injuries, thus one should try to avoid it at all times.


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For plastic pipes, the maximum admissible nominal pressure is often mentioned on the pipe itself; e.g. PN 6 means it can resist to a maximal nominal pressure of 6 bar (T.B. 2.30).


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The diameter mentioned on the nomograph is the inner diameter. Take this certainly into account for plastic pipes because their outer diameter is standardised in size, whilst their wall thickness depends on their resistance to pressure, and therefore has an influence on their inner diameter. For instance, the inner diameter of a PN 16 pipe is smaller than the inner diameter of a PN 6 pipe of the same external diameter (T.B. 2.30).


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➞ A velocity higher than 3.0 m/s might result in the particles eroding the pipe, and the risk of serious water hammering increases.


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The height difference H2 to determine the available pressure at the end tap, should normally be measured in between the water level of the spring / reservoir and the tap. As the water level of a reservoir can vary


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over time (getting empty, being refilled), it’s careful to keep the tank’s outlet as a reference because this doesn’t (really) change in height and it reflects the minimum pressure available.


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For gravity flow systems, the total head losses in mWC can never be higher than the height difference H2 in between the water source and the final outlet (e.g. tap). In case the calculated total head losses (in


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mWC) are higher than the available height difference (in m), the water supply system will regulate automatically its velocity, and therefore the flow will be lower than expected.


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The maximum pressure resistance of pipes for motorised pump systems should be more than the maximum pressure the pump can deliver (as such the pipes can’t burst, even with the pipe system closed / blocked and the pump at maximum pressure).


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Mark the future pipeline path clearly with pegs (and strings) to ensure straight lines. For long pipelines, this should normally have been done during or just after the topographic survey (T.B. 2.24). The pipeline should be kept as far away as possible from points where erosion can occur, like landslide areas, gullies and riverbanks.


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Dig the trench with its walls slightly inclined because complete vertical walls tend to collapse easier. The angle will depend on the type of soil. The dug out soil should be put a little away from the trench in order to avoid it would slide back into the ditch. The width at the bottom of the trench should be such that it permits the easy installation of the pipeline. Ideally, a distance of 0.3 m should be foreseen on both sides of the pipe. The strict minimum depth at which a pipe should be buried is 0.5 m, although that the ideal minimum depth is often considered to be around 0.8 m. In reality, the depth of the trench has to be chosen with the aim of protecting the pipeline against:


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➞ the weight of vehicles at motor road crossings: should be a trench dug of 1.5 m depth or the pipeline protected otherwise.


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➞ extreme temperatures: pipes can be protected from freezing or heat by laying them deeper in the ground.


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➞ erosion: the topsoil can erode over the years and the pipes might become exposed. Don’t open the trench too far ahead in advance as it can get damaged by erosion, and collect rainwater.


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Remove all rocks and stones from the inclined walls and bottom of the trench, certainly when plastic pipes will be installed because they might get damaged by them.


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Place preferably a sand bed layer of 0.05 m to 0.1 m (recommended) thick at the bottom of the trench, on which the pipeline can rest without any strain. In case the trench is situated in a very humid zone, the bed layer can be made with round pebbles (diameter of 5 to 30 mm) instead of fine sand, in order to drain the groundwater away underneath the pipeline.


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Lay the pipes in a slightly zigzagged manner inside the trench, together with their fittings and accessories (e.g. bends, valves), and connect them in the most appropriate way (T.B. 2.30).


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Do not leave a pipe end open or exposed so as to prevent it from dirt or animals like snakes getting inside. If nothing better is available, simple plugs made of tree branches can be used.


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Anchor all pipes to concrete blocks (thrust blocks) at bends, branch points, valves and at passages of steep slopes, to avoid that the joints would become loose due to the lateral forces where the flowing water changes direction.


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Backfill the trench as soon as possible to protect the pipe from the sun and vandalism. The backfill material should not contain organic material (such as sticks and bushes). The backfill material should ideally be slightly compacted at every layer of 0.1 m thick.


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Prevent rocks and stones to be dumped on the pipes. Only after the pipe has been covered by around 0.5 m of soil, stones and rocks can be used to backfill.


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Don’t cover the joint sections with soil until the pipe has been operated at full pressure and it has been inspected for leaking joints. If the joints are exposed to direct sunlight before they can be inspected, it will be good practice to temporarily cover them (with plastic sheeting for instance). After inspection the joints should be covered.


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Put markers (e.g. piles of stones cemented together) along the pipe line at regular intervals and all important points (e.g. the points were the pipe diameter changes, at direction changes or branch points). Identify the markers by using codes or numbers. If possible, make a sketch of the system, presenting all the available information.


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Plant short rooted vegetation (e.g. grass) on the backfilled trench to stabilise the soil and to protect it against erosion.


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Prior to the trench excavation and the installation of the pipes, issues related to land and/or water ownership must be taken into consideration and solved (T.B.1.04).


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A flat and levelled storage facility should be prepared nearby the construction area before the pipes arrive on site. The facility should have enough space in order that the piles of pipes don’t have to exceed 1.5 m in height. The moment the pipes arrive on site, they should be protected from direct sunlight. If the storage facility isn’t a closed shelter, the pipes should be covered. PVC pipes with push fit insertion joints (collars) should be stacked in an alternating manner to avoid deformation of the tubes and they must also be stored on a flat surface. It should also be avoided that the pipes have to stay too long on the site without being installed. The ends of the pipes should be closed to avoid dirt or animals getting in. The plugs have to be removed just before the pipes are installed.


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Care should be taken not to damage the pipes during handling, transport and storage on site. Contact with hard surfaces like stones, concrete or metal could damage the plastic and even the threads of GI pipes. It is therefore important to carry the pipes and not to drag them along, nor to drop them.


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In cold temperatures, plastic pipes get more brittle and therefore break easier. Specific precaution is needed during handling and transport.


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When the pipeline path follows a slope, it is better to start the work downhill and to progress uphill in order that runoff water can evacuate freely and the trench doesn’t get flooded.


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In some areas it will be impossible to bury the pipes due to the rocky underground. In these situations, it is preferred to install pipes that can endure shocks and harsh climatic conditions, like GI tubes. All aboveground pipes should be protected at places where heavy animals pass and at vehicle crossings.


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When the trench is less than 1 - 1.5 m deep at motor road crossings, the pipe without any joints should be embedded and covered by 0.2 m of sand. On this sand layer, a reinforced concrete slab of around 0.1 m thick should be poured. Above this concrete slab, the trench can be backfilled normally.


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In some circumstances (road or river crossings), it will be required to install the plastic pipes inside metal (e.g. GI) pipes with a bigger diameter. However, if a leak occurs in the PVC pipes, it will be difficult to localize it. It should also be avoided that dirt, stones or small animals can enter in the openings between the inner and outer pipes. This can be done by wrapping them in plastic sheeting.


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Pipes that are left in the sun, even when already installed, will heat up and expand, but they will contract again when they get buried or when cool water flows through them. To avoid that the contraction might pull the plastic pipes out of their sockets or fittings, they should be installed in a zigzagged manner. The UV-radiation of the sun makes the plastic pipes also brittle over time.


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Anchors and thrust blocks can be made out of simple cement blocks. The pipes and accessories (e.g. bends) can be anchored to the blocks by means of reinforcement iron bars.


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If the length of the path is important, dig the trench over 500 m, install the pipes and backfill the trench before doing the same on the next 500 m. Doing all the procedures over the whole length at once might lead to several problems: e.g. trenches collapsing, damages to uncovered pipes, theft.


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For pipelines of several kilometres in length, it is important to install sludge- and air valves. Sludge valves will need to be opened once in a while to avoid blockages from accumulated dirt / mud particles. Air valves might show their usefulness already from the beginning by removing air-locks when the pipeline is filled for the first time. An air-lock is an air bubble trapped in the pipeline, whose size is such that it interferes with the water flow through the section. They are formed when the pipeline is first constructed or when subsequently drained for maintenance purposes. Anyway, the design and installation of such long pipelines should be left to specialists.


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➞ Run potable water through the system until no visual dirt comes out anymore, and drain completely.


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➞ Add all this prepared 1% chlorine solution to a reservoir containing an amount of clean water equal to the pipeline volume and mix well to obtain hyper-chlorinated water.


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➞ Fill the pipeline completely with this hyper-chlorinated water. The process should be done slowly for the air to be able to escape, and with the end valves closed.


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➞ Drain the pipeline completely once the contact time of at least 24 hours is passed, and rinse with potable water.


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During an emergency, small air leaks on the suction side of a pump or other small leaks at the distribution pipes can be temporarily repaired with a 1 meter long (x 25 mm) inner tube wrapped tightly around the leak. The leaking pipe or joint should be properly repaired or replaced as soon as possible.


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<table><tr><td>In a large number of emergencies, water trucking is used as a temporary measure to provide water to the</td></tr><tr><td>beneficiaries. The installation of more sustainable solutions can be time consuming and an urgent need</td></tr><tr><td>for water often necessitates trucking in the initial stages. However, water trucking is expensive, often</td></tr><tr><td>difficult to organise and to maintain, thus it should be avoided if feasible or replaced as soon as possible.</td></tr><tr><td>In most settings, the development of an alternative water supply system will be cheaper in the long run.</td></tr></table>


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In a large number of emergencies, water trucking is used as a temporary measure to provide water to the beneficiaries. The installation of more sustainable solutions can be time consuming and an urgent need for water often necessitates trucking in the initial stages. However, water trucking is expensive, often difficult to organise and to maintain, thus it should be avoided if feasible or replaced as soon as possible. In most settings, the development of an alternative water supply system will be cheaper in the long run.


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Determine the volume of water to be supplied (see example hereunder) and preferably add 10-20% to allow for losses and new arrivals. Losses will vary according to different factors like the quality of equipment (e.g. leaking taps / tankers), the mode of water collection (e.g. jerrycans with cap versus open buckets without lid), the type of delivery point.


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Synchronise where possible the water delivery with the peak demands of the beneficiaries (e.g. early morning and early evening).


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Select a water source taking into account its yield, its proximity to the delivery point, its access for trucks and its water quality. The loading site of the water source should have enough space to allow easy filling of the trucks and if needed, the installation of a treatment system (e.g. assisted sedimentation; T.B. 2.16) or of a storage infrastructure (e.g. for a low yielding source).


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Select the size and type of vehicle, taking into consideration the road conditions (e.g. the load-bearing limit of the road surface, slippery surfaces, steep slopes, tight corners, narrow tracks). Bladders fitted on flatbed trucks or mounted on tractor pulled trailers are a good alternative to water trucks. Solid plastic tanks can also be used, but special attention has to be given to the fact that they will modify the centre of gravity of the truck drastically. Generally, the greater the capacity of the trucks, the more efficient the process is, as long as the road conditions permit the use of big vehicles.


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Calculate the size of the fleet needed by following the steps of the example hereunder. Incorporate a safety factor in the design if the transport fleet is not that reliable, like a back-up vehicle or additional storage capacity at the delivery point.


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Inspect, clean and disinfect with a 0.1% chlorine solution (T.B. 2.20) all the tankers and any associated piping or pumps before use. Rinse them well afterwards with clean disinfected drinking water to remove the chlorine residuals. Avoid tankers that have previously been used to transport oil, fuel or chemicals and opt instead for dairy or brewery type tankers.


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Hire lorries for water trucking on the basis of either a set time frame (e.g. per month), or on the quantity of water delivered (e.g. per trip of a tanker of known volume). Hiring per quantity of water delivered requires greater monitoring, but motivates the contractor to meet the agreed targets.


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Make contracts and sign them (prior to the start-up of the work), clearly stating the responsibilities of both parties in terms of insurance (in case of accident), vehicle maintenance, fuel and lubricant costs, labour (driver and his helper). In terms of management, it is recommended that the contractor takes on all these responsibilities for a reasonable premium.


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Make sure that the drivers follow the organisational rules and that the vehicles correspond to the regulations of the specific country.


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Ensure adequate funding for the specified time frame on the basis of a detailed budget, because the running costs of trucking operations are often high.


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Include also more hidden costs like maintenance of loading and delivery points, installation and running costs of storage and treatment facilities, and salaries of watchmen, fleet managers, chlorinators.


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Monitor the quantities delivered and to which water points. A centralised monitoring system will be required in large operations, particularly in situations where different partners are involved.


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Summary: A total of 7 trucks with a carrying capacity of 5,000 litres each will be required to make 6 trips per day to supply 15 l/person day to 12,000 people. The selection of 8 tankers, rather than 7, adds a degree of security in case of a breakdown of one of the other tankers.


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Chlorination within the water truck can save a lot of time because the contact time needed for the disinfectant (T.B. 2.21) can start already during the transport.


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If chlorination of the water has to be done in the trucks, a 1% chlorine mother solution (T.B. 2.20) has to be prepared (only add the supernatant, not the potential calcium deposits). The quantity of chlorine that has to be added per truck should be evaluated by a chlorine jar (modified Horrocks) test (T.B. 2.21). If tankers are metallic, the Free Residual Chlorine (FRC) concentration should be verified at the destination and the chlorine concentration adapted accordingly if needed.


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The selection of water distribution points should be made on the basis that water will be supplied by tankers: ease of tanker access will be the main consideration. Avoid time-consuming offloading procedures like pumping water from tanker to storage tank over extended distances.


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Offloading must be done from the truck to the reservoirs and not directly to the beneficiaries because the latter wastes too much time. It’s better that the water truck can leave as soon as possible to fetch another batch of water.


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Efficiency is often an area of weakness in water trucking operations. Attention should be given to reduce the turn-around time and water losses, and to avoid bottlenecks. For example, pumps can be used to reduce the time needed to offload tankers. Having a pump as well as telecommunication means in every truck can thus be considered as advantages.


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If security permits, the trucking should start and stop well beyond the times people collect the water, in order to comply with the peak demands (so potentially have two periods of water trucking of about 6 hours each, around the peak demand periods).


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Given the high costs of water trucking over an extended period, a firm commitment to develop more appropriate water supply solutions for the medium and long-term must be taken. It may involve the development of new water sources and/or transport means (e.g. installation of a pipeline), or the improvement of existing ones.


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<table><tr><td>Type</td><td>Capacity m3</td><td>Set up</td><td>Use</td><td>Remarks</td></tr><tr><td>Bladder (pillow tank) Closed tank</td><td>0.85 2 5</td><td>-Very easy and fast to set up - Mountable on a flatbed truck</td><td>Storage Chlorination Transport</td><td>Static or mobile Difficult to clean</td></tr><tr><td>Bladder (pillow tank) Closed tank</td><td>15</td><td>- Very easy and fast to set up</td><td>Storage Chlorination</td><td>Static Difficult to clean</td></tr><tr><td>Onion tank Self sustaining open tank with roof</td><td>30</td><td>-Very easy and fast to set up</td><td>Storage Chlorination (Assisted) sedimentation</td><td>Static Relatively difficult to clean</td></tr><tr><td>Liner tank supported by metal frame Open with roof</td><td>10 30 60</td><td>- Easy and relatively fast to set up</td><td>Storage Chlorination (Assisted) sedimentation</td><td>Static Easy to clean when mounted</td></tr><tr><td>Corrugated iron sheet tank with a separate lining Open with roof</td><td>11 45 70 95</td><td>Least easy to set up Bulky transport because of corrugated sheeting</td><td>Storage Chlorination (Assisted) sedimentation</td><td>Static Easy to clean when mounted Less suited for acute emergency Longer life expectancy</td></tr></table>


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Type Capacity m3 Set up Use Remarks Bladder (pillow tank) Closed tank 0.85 2 5 -Very easy and fast to set up - Mountable on a flatbed truck Storage Chlorination Transport Static or mobile Difficult to clean Bladder (pillow tank) Closed tank 15 - Very easy and fast to set up Storage Chlorination Static Difficult to clean Onion tank Self sustaining open tank with roof 30 -Very easy and fast to set up Storage Chlorination (Assisted) sedimentation Static Relatively difficult to clean Liner tank supported by metal frame Open with roof 10 30 60 - Easy and relatively fast to set up Storage Chlorination (Assisted) sedimentation Static Easy to clean when mounted Corrugated iron sheet tank with a separate lining Open with roof 11 45 70 95 Least easy to set up Bulky transport because of corrugated sheeting Storage Chlorination (Assisted) sedimentation Static Easy to clean when mounted Less suited for acute emergency Longer life expectancy


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Choose a site for the installation, ensuring that the reservoir will be accessible under all circumstances and at all times to be able to fill it (e.g. by water trucking). A reservoir filled with water is heavy (e.g. about 15 ton for a full 15 m3 bladder) and needs to be installed at a safe location where it can’t cause accidents (e.g. a filled reservoir rolling down a slope, or a bladder on top of a non-reinforced flat roof). Discussions with the different stakeholders must also be undertaken when choosing the site.


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➞ using the natural slope of the terrain or a safe existing construction. This method allows a relatively rapid installation of the reservoir. But the slope should not be too steep and might need to be excavated to have a flat base. The existing construction on the other hand should be strong enough not to collapse under the heavy weight of the filled reservoir.


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➞ constructing a platform strong enough to withstand the heavy weight of the filled reservoir. All kinds of material can be used to construct a platform: e.g. compacted earth with sloped embankment, oil drums


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(the drums at the perimeter filled with stones or soil for stability), sand bags, wooden beams and planks, (cemented) boulders, gabions. In case such material would only be available in limited amounts or that it would become too expensive, it’s possible to use it only for the outer hull of the platform and fill the inside with stones and/or earth.


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➞ putting the reservoir straight on the ground without a height difference and supply the tapstands with water by means of a hand pump or a motor pump. This system has the advantage that it can be installed


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very quickly with a minimum of preparation. When a motor pump is used, the distribution system can easily be extended, but it consumes fuel.


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The base for the reservoir should be flat and larger than the surface of the empty tank (a minimum free space of 0.3 m all around the tank should be foreseen). The base should be cleared of all objects that could puncture the tank (e.g. stones, sticks, nails) and if possible, covered with a layer of sand.


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Put the tank (the liner and the potential frame) on the groundsheet, taking into consideration the direction of its outlet(s). In case of a frame, assemble it and connect the flexible tank liner according to the manufacturer’s instructions.


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Verify if the outlet valves of the reservoir are well tightened and adjust if needed (the manufacturers don’t always tighten them very well, or haven’t even installed them at all). Teflon tape can be used to avoid leaks at this level.


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Organise the distribution point(s) by installing the tapstands (T.B. 2.39). An alternative for very short term distribution is to use the ball valves that are supplied in certain kits.


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Install a drainage system around the reservoir’s base and around the distribution point(s) to avoid rapid deterioration of the sites.


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Install a shadow net, or a roof made of local vegetation (e.g. banana leaves) or plastic sheeting over the reservoir to protect it at least against direct sunlight. This helps to avoid that the water in the tank gets warm. It will also protect the plastic liner against UV-irradiation, which renders the material brittle over a prolonged period. For very harsh weather conditions (e.g. freezing temperatures), special protective measures have to be taken. In such cases, contact your technical referent.


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Build a fence to avoid kids playing with or on the (flexible) reservoir. It is also strongly recommended to have an attendant at the reservoir for safety, operation and maintenance.


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In order to avoid abuse of the (flexible) reservoir, it is recommended not to have it too close to the distribution point(s). However, the longer the distance, the higher the head losses in the delivery pipe(s) and the lower the flow (T.B. 2.31) will be. This is certainly important when a platform needs to be build because the higher the head losses, the higher the reservoir needs to be. Also when the water is delivered from the reservoir to the tapstand via a hand pump, the distance should be restricted.


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Bladders can be filled via the central opening or via one of the side connections. In the latter case, the cap of the central opening must be unscrewed and put loosely on top, allowing the air that is trapped inside the reservoir to escape, but without dirt entering. Do not overfill the tank: when water is overflowing via the central opening, the reservoir is full.


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When water is pumped from the reservoir to a tapstand by means of a motor pump, a recirculation system from the pump directly back to the reservoir must be installed (as per figure B). This is to avoid that the pump and the water inside would heat up when all the taps are closed. Failing to have a recirculation system can potentially lead to personal injury (burns) and will eventually break the pump. In cold weather, this recirculation system also reduces the risk of the water starting to freeze in the reservoir and the pipes.


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When rationing the water, the gate valve(s) of the reservoir can be closed and the knob removed. Be careful not to loose the knob.


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After use, it is essential to clean, disinfect and dry the tank completely before repacking it (T.B. 2.37). Do not fold the tank until it is completely dry (takes 2 - 3 days of drying, at least).


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To repair the reservoir, use the repair module that is included in the kit and follow the instructions carefully.


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Metal construction scaffolding can be used to construct a water tower, permitting the relatively rapid installation of reservoirs on rather high elevations (e.g. 3 m). Only professional scaffolding should be installed on a solid underground (preferably concrete foundation) to avoid the risk of collapse once the reservoir is filled. This solution could be particularly interesting where a centralised water supply system is required (e.g. in a health structure).


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Check the reservoir for leakages or other damages (e.g. faulty connections). Repair them when needed and if it is still possible. The check up for leaks is easiest by filling the reservoir completely with water. In case of holes, fix them with the repair material included in the kit, according to the manufacturer’s instructions.


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Put the groundsheet of the reservoir on a big, clean, flat but slightly sloped surface (e.g. tarmac, concrete). Make sure that the sloped surface has a drainage system at its bottom.


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Wet the groundsheet with clean, non-salty water, clean it on both sides with water and liquid soap by means of a soft brush and rinse it to remove all dirt and soap residues. It is possible that some force will have to be used to remove all dirt.


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Wet the reservoir with clean, non-salty water, clean it on all outer sides with water and liquid soap by means of a soft brush and rinse it to remove all dirt and soap residues. Before flipping the reservoir over to clean the bottom side in a similar way, it is recommended to rinse the groundsheet again in order to avoid that dirt coming from the bottom of the tank would be transferred to its cleaned side.


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Move the bladder and its groundsheet to a big, clean and completely flat surface (e.g. tarmac, concrete).


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Once installed and the side opening(s) closed, fill the bladder with some clean, non-salty water in order to get an even thin water layer of 2 - 3 cm thick.


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Rub the upper side of the bladder against its bottom side in order to loosen all the dirt inside. Special attention should be given to the corners of the bladder.


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Keep repeating these actions until no dirty water comes out of the bladder anymore. When the inside of the bladder would stay dirty (e.g. high presence of algae or a bio-film), a certain amount of 1% chlorine mother solution can be added (e.g. 20 l for a 2 m³ bladder, 40 l for a 5 m³ bladder and 100 l for a 15 m³ bladder; T.B. 2.20) when a new thin layer of clean non-salty water is introduced. This high chlorine concentration should help to remove the organic material.


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Add some 1% chlorine mother solution inside the bladder (10 l for a 2 m³ model, 20 l for a 5 m³ model and 50 l for a 15 m³ model) when a new thin layer of clean non-salty water is introduced, with the intention to disinfect the reservoir. The solution can be drained from the reservoir after at least 30 minutes.


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Rinse the reservoir inside and out for a last time with clean, non-salty and disinfected water, as well as its groundsheet.


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Turn the reservoir (liner) inside out on its clean groundsheet. For a reservoir with a (corrugated sheet) frame, it’s often easier to clean and disinfect the inside of the liner when it is still mounted.


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Wet the inside of the reservoir with clean, non-salty water and clean it with water and liquid soap by means of a soft brush.


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Rinse the reservoir thoroughly with clean, non-salty water until all dirt and soap residues have disappeared.


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Disinfect the inside of the cleaned open reservoirs by means of a clean cloth or sponge soaked in 0.05% chlorine


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solution (T.B. 2.20). When a sprayer is available, it can be used as an easy alternative to disinfect the reservoirs.


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Rinse the groundsheet and the reservoir (inside and outside) for a last time with clean, non-salty and disinfected


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Dry the reservoir properly, preferably in a non-humid environment (e.g. inside a building to avoid that it gets wet by the rain). The drying can be done by hanging the reservoir up without touching the ground, whilst the different surfaces of the plastic liner (bottom and upper sides of a bladder, bottom and vertical sides of an open tank) should stay well separated from each other. When possible, have all the openings open and pointing downwards so the water can drip out easily. In case a compressor is available, blow compressed air into the (bladder) reservoir to dry it.


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Put some talc powder in and on the reservoir in order to absorb the last humidity, once the reservoir seems completely dry.


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Fold the reservoir properly and store it in a solid crate, together with all its accessories. The crate is preferably made out of metal to protect the liner against rats biting holes in it. Make sure that the solid elements of the reservoir can’t damage its plastic liner; e.g. the couplings should be covered with some cardboard or with the plastic envelop that sometimes is issued by the manufacturer.


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Make sure that the cleaners wear their appropriate protective gear (an overall, rubber boots, rubber gloves, goggles or a face shield), certainly when they are working with chlorine (as chlorine splatters might cause injuries).


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Salty water cannot be used because it could corrode the valves and leave salt residues on the reservoir and groundsheet.


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Make sure that all openings of the bladder tanks are well closed during its external cleaning to avoid soap getting inside. If some residuals of the soap would stay behind in the bladder, it could give a bad taste to the water when the reservoir would be put in use again.


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The internal cleaning of the 15 m³ bladder can be started by pumping clean, non-salty water across the reservoir. The water should enter via one side opening and leaving via the opposite opening. The flow rate of the pump should be adapted to the evacuation rate at the opposite side (the reservoir should not start to swell up). The pumped water will remove already the first dirt particles from the tank. The pump period shouldn’t take too long and can be stopped when the first wave of really dirty water has been evacuated. The same principle can be repeated once more in the opposite direction. The rest of the internal cleaning should be done as described above.


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A soft brush on a stick can sometimes also be helpful to clean the inside of the smaller bladder models. However, a very flat surface is needed to be able to clean it with this method.


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The easiest way of cleaning onion tanks is to clean the outside wall first, turn it upside-down and clean its bottom, then turn it inside out and repeat the same procedure again (first the inside wall that has come on the outside now, then the bottom). In between each step, the reservoir and groundsheet should be well rinsed. This procedure ensures that no spots of the tank will be missed. This principle can also be used for flexible reservoirs with a support frame in case they wouldn’t be installed any longer.


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Some brands provide specific features to ease the hanging of the reservoir (e.g. special reinforcements at the corners of bladders, as per figure C; a big internal central ring on some onion tanks). Bladders that don’t have these features can be hung over a long smooth metal bar or a bamboo stick and lifted from the ground by means of ropes (as per figure B). A better alternative is to use a smooth metal pipe (+/- 1 m long) that is introduced inside the reservoir through its central opening and then hoisted from the ground (as per figure A). The advantage of this system is that the upper and bottom sides of the reservoir can be separated from each other for better drying. The edges of the pipe should be protected with a cloth to avoid puncturing the liner.


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Make sure that all accessories of the kit are present before starting to repack (e.g. hoses, valves, all the bolts and nuts of reservoirs with a frame). If parts are missing, they should be replaced


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Before taking the used and cleaned reservoirs in use again, rinse their inside with some clean and non-salty water to remove all the talc powder.


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Drive stakes vertically into the ground, forming a circle of 1.2 m in diameter. The centres of the stakes should be spaced about 0.2 m from each other, leaving at least 1.5 m of their length aboveground.


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Wind three thicknesses of wire mesh around the circle of stakes. Stretch and flatten the layers of mesh well against each other and fix them to the stakes and to each other with fine wire.


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Reinforce the structure by winding round it three turns of thick wire: at the top, in the middle and at the bottom.


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Push a length of galvanised iron pipe with a valve attached through the mesh near the bottom (for draining), and another one diagonally above with a valve or tap for the outlet. In case water is taken directly from the tank, there should be high enough space in between the ground surface and the tap to be able to put containers underneath. A third pipe for the overflow is fixed near the top of the tank.


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Apply a 10 mm first coat of cement plaster (T.B. 2.05) to the outside. One person should be on the inside to retain the mortar with a float as it is applied. Leave it to harden for 12 to 24 hours, keeping it damp.


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Apply a 10 mm coat of cement plaster to the inside so as to cover the mesh completely. Leave it to harden for 12 to 24 hours, keeping it damp.


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Apply a finishing coat (smooth cement plaster; T.B. 2.05) to the inside and the outside and smooth well.


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Cover the bottom of the tank with wire mesh and curve it up at the corners where the walls meet the bottom.


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Choose the site to install the tapstand(s). The site should permit a good drainage for rain and spilled water, and should be easily accessible for the users, specially for vulnerable groups.


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Construct an apron with protective kerb at the chosen tapstand site, made with stones and covered with cement plaster (T.B. 2.05), or preferably lean concrete (similar to T.B. 4.02). This apron should drain the spilled water away and thus avoid mud and stagnant water near the water point. The spilled water should be disposed of via a soak away pit (T.B. 4.06), an infiltration trench (T.B. 4.07) or an evapo-transpiration area (T.B. 4.08). If the spilled water is not mixed with grey water (water coming from washing laundry or dishes on the apron), it doesn’t need to pass via a grease trap, and it could also be used to irrigate a vegetable garden.


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Assemble the tapstand in such a way that the distance in between the nozzle of the taps and the apron is slightly higher than the biggest water recipient in use by the beneficiaries (often a gap of 0.5 m is sufficient). This limited distance will reduce the amount of water falling next to the recipient, especially in windy places. For people (e.g. children) who often come to collect water with small (e.g. 5 litres) jerrycans, a small stand can be made under one or two taps.


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Connect the tapstand to the reservoir. Ensure a correct pressure and flow at the taps by creating the right height difference between the tapstand and the reservoir and/or by choosing the right type and proper diameter of pipe (T.B. 2.36).


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➞ A too high pressure can make it difficult (for children) to open the self-closing taps, and it can create a water


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➞ A too low pressure might result in a flow rate below the desired yield, and it can increase the leaking of certain self-closing taps.


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An alternative is to provide an artificial pressure and flow by means of a hand pump or a motor pump (T.B. 2.36).


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In case the tapstand is connected to the reservoir with a non-collapsible pipe (e.g. Heliflex pipe), it is strongly recommended to bury it, even in an acute emergency.


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If several tapstands are to be installed at the same place, separate them enough to avoid beneficiaries pushing and shoving at busy times. The bigger reservoirs have two outlets, so it is possible to install a tapstand at each end to have two distinct distribution points. Also a tapstand supervisor can be appointed to avoid problems.


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To connect two tap-stands in series, undo the stopper from the Tee of the first tapstand and connect it with a piece of (Heliflex) pipe to the inlet of the second one. To have a good flow at all taps, do not place more than 2 tapstands in series.


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To ensure a minimum flow of around 10 l/min from each single self-closing tap, a nearby reservoir should be installed at least 1.2 - 1.5 m above the tapstand.


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In case the water flow at the tapstand would be too high (risk of big splashes), it can artificially be reduced by installing a partially closed gate valve at its inlet.


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Check from time to time that the taps close properly. Solid particles in the water or objects inserted by users may prevent correct closure and therefore will increase water losses.


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When a soak away pit is chosen to dispose of the waste water, allow a minimum distance of 3 m away from the tapstand.


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During the first days of an acute emergency, the evacuation of the spilled water can be done via a gravel pit, while constructing a correct apron.


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Human excreta transmit many infectious diseases. The pathogens leave the body of the infected person via the excreta and can then be transmitted to healthy individuals. This problem is particularly acute in health care facilities due to the high number of sick people present and to the high level of infectiousness of their excreta.


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Pathogens are transmitted by direct contact (hands) and domestic contamination (water, food and objects contaminated by excreta). Pathogens may be viruses, bacteria, protozoa and certain helminths. The list of faeco-orally transmitted diseases includes notably amoebic dysentery, cholera, giardiasis, hepatitis A and typhoid fever.


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Helminth eggs have a latent period between the moment they are excreted and the moment they become potentially infectious. The transmission of these “geo-helminths” takes place through the contamination of soil and/or crops. It mainly concerns ankylostoma, ascaris and strongyloides. Infection by these helminths is very frequent and the prevalence may be higher than 90% in certain populations.


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Cattle and pigs are intermediate hosts of taenia. The transmission cycle involves the contamination of soil and forage by human excreta, then the ingestion of undercooked meat by humans.


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The excreted eggs of those helminths pass part of their life cycle in one or several intermediate aquatic hosts (snails, crustacean, fish), before becoming infectious to humans. An example is schistosomiasis. Its transmission cycle involves the contamination of surface water by human excreta, development within a snail host and finally the penetration of the skin of a new human host when he enters the water.


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This includes all the diseases, which can be transmitted by “insects” like flies and mosquitoes, which breed in environments containing excreta (e.g. Culex pipiens mosquito that transmits filariasis).


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The term “excreta” includes urine and faeces. Urine is less dangerous than faeces, except in the case of typhoid, paratyphoid, leptospirosis and one type of schistosomiasis (Schistosoma Haematobium). The main objective of safe excreta disposal is to reduce the transmission of diseases due to environmental contamination by faecal matter or the proliferation of vectors. This objective can mainly be reached through excreta containment.


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The health impact of excreta disposal activities is difficult to evaluate however. It is generally agreed upon that a health impact will only be achieved if these activities are linked to improved water supplies, and individual and collective hygiene. It might also be necessary to combine excreta disposal with vector control methods (e.g. spraying).


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For each of the five types of excreta-related diseases, following respective control measures can be proposed (see table hereunder):


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Control measuresFaeco-oraltransmis- sionHelminthstransmitted by soilBeef andpork tapewormsWater-based helminthsInsectvectorsSafe excreta disposal(providing latrines / toilets)XXXXXcombined with vector controlImprovement of waterquantity and quality (e.g. boiling of water)X----Improvement of shelterconditionsX----Improvement of hygienepractices (e.g. hand washing, covering food)X---XHealth promotionXXXXXTreatment of excretabefore its use for fertilizing cropsXXX--Inspection and thoroughcooking of meat--X--Inspection and thoroughcooking of fish and aquatic plantsX----Control of intermediatehosts (e.g. snails in irrigation canals)---X-Reduction of contact withpotentially contaminated water---X-


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In the first phase of an emergency, where there is a large concentration of people (e.g. refugee camps, collective centres), or where the normal sanitation structures are destroyed due to a (natural) disaster, it is essential to provide simple defecation facilities immediately. These facilities are provisional and need to be improved or replaced progressively over time by more suitable structures as the situation develops into a chronic emergency. In chronic emergencies as in stabilized situations, factors like local practices and socio-cultural issues should dictate the choice of the techniques used.


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In the first phase of an emergency, the aid-agency will often have to implement and to maintain (cleaning and repairing) the facilities. In chronic emergencies and certainly in stabilized situations, community participation will be essential for correct excreta disposal management. In those cases, the users should be included as much as possible in the choice, the implementation and the maintenance of the excreta disposal facilities. The authorities can also have an impact on the choice of the excreta disposal method, because standardised facilities are desired, for example.


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It should be verified if the users can provide their own anal cleansing material. If not, the aid-agencies might have to supply appropriate material that doesn’t fill up the latrine pits too fast.


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A gradual improvement of the excreta disposal facilities is also valid for health structures, even if those facilities will have to be conform to the essential requirements (T.B. 1.08) already from the start (e.g. upgrade from improved trench latrines to simple pit latrines). Appropriate material for anal cleansing should be readily available.


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Correct sanitary facilities are extremely important for female teenagers and adults, certainly during their period. It might therefore be important to integrate washing basins and drying lines within female sanitary blocks, for the ladies to be able to wash their reusable sanitary towels. A waste bin in the neighbourhood of the sanitary facilities is essential for the disposal of (single use) sanitary towels.


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For correct planning and organisation of safe excreta disposal, it is necessary to follow all the different steps described in chapter 1. Some specific points of the assessment phase directly related to excreta disposal are gathered below.


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As only simple and temporary excreta disposal solutions will be chosen for the first phase of the emergency, the information needed before implementation is limited and can be collected during the initial assessment. Some basic data on the physical nature of the site, the demography, the anal cleansing habits of the population and the material available are sufficient to determine the first phase strategy.


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An in-depth assessment with the participation of the users will be needed to define a safe excreta disposal strategy for chronic emergencies and stabilized situations. For facilities to be fully functional, a lot of information needs to be collected and analysed. In general the choice of an excreta disposal technique depends on:


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Socio-cultural and religious factors: particularly traditional and local attitudes and practices concerning excreta disposal:


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➞ Soil: type; available depth and ease to excavate; infiltration rate; stability; resistance against weight (heavy superstructure).


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➞ Water: availability in sufficient quantities (in case of anal cleansing with water and pour-flush latrines); different resources and their proximity (risk of pollution); level of the water table and its seasonal variations (risk of pollution); natural drainage of runoff water; risk of flooding.


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➞ Materials and tools (if locally available, there will be an impact on the construction time and costs, but also on the environment).


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The system should be chosen with all this information in mind, whilst remaining simple, cheap and above all easy to install and maintain (by the population / beneficiaries).


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There are many excreta disposal techniques. In each situation the chosen technique should be adapted to the context, the site conditions and the users (their culture and habits). If these issues are ignored, the facilities will most probably become unused after a while and/or get damaged. The sanitary facilities may even create a health risk by themselves.


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➞ Gender has to be taken into consideration (separate excreta facilities for men and women might have to be constructed, certainly in public buildings like schools and health structures).


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➞ Special facilities for menstruating women and girls might have to be considered (e.g. discrete washing places for sanitary towels).


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➞ There should always be a separation in between the excreta facilities of the staff and the patients


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➞ Situated at such a place to prevent sexual violence (close enough to buildings / dwellings, lights available during the night time).


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➞ Handicapped and physically impaired people may need specifically adapted excreta disposal facilities in terms of distance, available space, equipment (e.g. handrails, seats). The design of these facilities will mostly be done on a case-by-case basis.


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➞ The distance that infected people (e.g. HIV / AIDS) can cover are limited, thus the excreta facilities should be close by.


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It respects cultural requirements; besides the defecation position, the superstructure itself can have an influence if a facility is used or not:


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➞ Some cultures want it to be open, but most prefer to have privacy and thus a superstructure, with or without a roof (also depending on the type of latrine and rainfall).


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➞ Doors are not always available or affordable, so it should be checked if a spiral-shaped superstructure without a door is acceptable.


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➞ Local materials should be chosen as much as possible, as long as this doesn’t have a too negative impact on the environment (e.g. deforestation).


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For excreta disposal facilities to be more effective and to increase the public health benefits, they should be maintained regularly, and hand-washing equipment (including soap or ashes, and water) should be available.


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To have an impact with safe excreta disposal, it’s important to rehabilitate the formerly used “wild defecation areas” once better facilities are at hand.


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Defecation fields (T.B. 3.01) may provide a very short term emergency solution, particularly in hot dry climates and where there is enough space available.


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Trench latrines (T.B. 3.02) may also be an adequate solution for acute emergency situations. The advantages over a defecation field are that the faeces are already better contained and possibly covered by the user with soil (located alongside the trench). The reduction of required space is another advantage.


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Improved trench latrines (T.B. 3.03) are simple and rapid to build, certainly when prefabricated (plastic) slabs are available. Therefore, they can still be constructed during the first phase of an emergency. The slabs reduce the risk of people falling into the trench and the accessibility for flies is limited, at least if the lid is replaced on the slab. As the superstructure is divided in different compartments, improved trench latrines offer already about the same privacy as simple pit latrines. Combining some features of the trench latrines (simplicity and rapidity to construct) and the simple pit latrines (privacy, already improved safety), the improved trench latrines are an interesting intermediate solution. They are also the minimum option for health structures during acute emergencies.


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If an auger or (hand) drilling equipment is available, a borehole latrine covered with a simple slab may be installed rapidly. Be aware however that the faeces often stick to the sides of the upper bore part, thus increasing the risk of attracting flies and augmenting the likelihood of blockages. Additionally, borehole latrines can only be made in areas with a very low water table (even during the rainy season).


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In some parts of the world, defecation in plastic bags is a common practice (e.g. in slums where no latrines are available). In certain situations (e.g. lack of space in flooded areas, difficulties to dig in the debris after an earthquake), and if it is socio-culturally acceptable, this practice might be the only feasible solution during the first phase of an emergency. The bags should be biodegradable and preferably specially designed for the purpose (e.g. adapted shape and capacity, containing a specific product accelerating the biodegradation and/or absorbing the liquids). Obviously, the bags have to be collected, transported and disposed of (burial) in a safe manner. As the bags should be closed after use with a knot, the health risks are less compared to the collection of night soil in buckets, which is another common but unsafe practice in some places.


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Whatever the emergency solution chosen, it is important to take steps to ensure that the facilities work well, are maintained properly and are utilised by the beneficiaries. Promotion campaigns and support from the local leaders are therefore essential. Hand washing equipment nearby the excreta disposal facilities should not be forgotten, even in acute emergencies.


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Where simple means are used in the first stages of an emergency, different disposal techniques may be used in the later phases of an emergency and in stabilized situations. There is no formula to suit all circumstances. But based on the collected information as described above, it should be possible to choose the most appropriate solution that remains simple, cheap and above all, easy to install, to use and to maintain (possibly by the population / beneficiaries).


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Simple pit latrines (T.B. 3.04) are the most common excreta disposal facilities to be found in population settings, because they are rather quick and easy to build. As these facilities are built to last for a longer time span, more attention should go the pit and its lining, the slab (T.B. 3.05) and the superstructure. Often, small children cannot use a normal simple pit latrine due to the size of the defecation hole and the position of the foot rests. They are often also afraid to be enclosed inside the superstructure. Therefore is it important to implement children’s pit latrines (T.B. 3.06) as well, specially in health structures where lots of children are present (e.g. feeding centres, paediatrics ward).


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Ventilated Improved Pit (VIP) latrines (T.B. 3.07; 3.08) are mainly interesting for long-term settings, such as public buildings like schools and health structures. Their ventilation pipe with flytrap is a big advantage as it reduces considerably odour and fly nuisances. However, VIP latrines are rarely the ideal option in population settlements within chronic emergencies because they are rather difficult and expensive to build, certainly by families themselves without any support. Children might also be afraid to use a VIP latrine because of the semi-dark environment that has to be kept in its superstructure for proper functioning.


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Twin pit latrines (T.B. 3.09) consist of two completely separated (VIP) latrines, of which only one is operational at the time. Once the first (VIP) latrine pit is full, the second one can be opened for use. When well designed, the full pit can be emptied manually, but only if a period of minimum two years has passed since it was last used. This minimum period is for the excreta to become completely harmless. This has the advantage that twin pit latrines can be used over and over again without any health risks. This can be extremely interesting for health structures in stabilized situations. However, in many cultures there are taboos related to the handling of excrement residues. It also requires a certain knowledge or training to use them correctly. The initial investment is considerable and therefore are twin pit latrines rarely used at family level. This kind of latrines can be used as / transformed into ecological sanitation facilities.


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Dehydration sanitation (separation of urine and faeces) and aerobic composting latrines (adding domestic organic waste and aerating) are ecological sanitation (Eco-San) systems which should shorten the period before human waste can be handled safely. However, they are only to be implemented in areas where they are already known and practiced, or when a complete long-term latrines project is started with a serious integrated promotion campaign. They are mostly not appropriated for emergency situations.


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Raised pit latrines (T.B. 3.12) above the ground level are one of the options to provide adequate sanitary facilities in difficult circumstances (e.g. high water table, flooding, rocky underground). However, a raised pit is often more difficult to build and the costs are often higher. Simple pit latrines, VIP latrines and twin pit latrines can all be raised.


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Pour-flush latrines (T.B. 3.10) can be very interesting for populations that use water for anal cleansing, certainly as the siphon forms a seal that reduces the odour and fly nuisances. If the design is well made, it requires very little water to flush the latrine. However, enough water should be available in the direct neighbourhood to consider this option, certainly in settings with a lot of people. It is recommended as well to use the system only if the population is familiar with this technology, or when there are time and resources enough to promote their correct use and maintenance. Pour-flush latrines should be completely avoided when people are using solid materials (maize cobs, stones, leaves) to do their anal cleansing, as they will block the siphon rapidly.


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Septic tanks (T.B. 3.11) connected to pour-flush latrines or flush toilets will separate the solids (faeces) from the liquids (mainly water). The faeces will decompose an-aerobically within the septic tank, whereas the liquids need to be evacuated. As these liquids still contain a lot of pathogens, a decent infiltration or a closed sewer system will be needed to avoid health risks. Some septic tanks are foreseen with a percolator which treats the liquids to a certain extent, reducing the amount of pathogens before disposal.


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Secondary wastewater treatment and complete sewage systems fall out of the scope of these guidelines.


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Maintenance is a key element in the use of excreta disposal facilities. A dirty latrine will certainly not be used. Hand washing facilities with soap (or ash) nearby the latrines are essential to reduce the hazard of faecal-orally transmitted diseases.


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In the first phase of an emergency, public facilities are most often the only viable option for “safe” excreta disposal, because they have to correspond rapidly to a minimum level of quantity and quality. Also in chronic emergencies, this minimum level may only be obtained when public facilities are built by aid-agencies. Linked to the specific physical nature of the site (e.g. limited availability of space, high water table, rocky ground), it might be (technically) impossible for the people to construct their own latrine. Non-precarious situations may also require public facilities, like:


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However, when a public facility is adopted for a population or for a central service (e.g. a hospital), it is indispensable to appoint a team that is responsible to ensure correct maintenance. This team will probably have to be remunerated for this service. The main advantage of family latrines over public facilities is the fact that they normally pose fewer maintenance problems. People normally take more care of their own latrine and have fewer problems with cleaning the dirt of their family members than of total strangers.


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As family latrines are mostly closer to the dwellings, the chance of actually being used improves, certainly when the people themselves have built them. The smaller distance increases also the safety, certainly for women and girls as they may be victim of sexual violence when they go to the latrine (at night). It might be easier to persuade people to dig their own individual family latrine if a good promotion campaign is done and when construction material is (made) available.


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If family latrines are not possible because of the population density or due to a lack of resources, an alternative is to construct one latrine per lot of three or four dwellings (or about 20 people), called a cluster latrine. The advantages are that the distances stay small and that the latrine is used by people who know each other and therefore can make arrangements for the maintenance. Another alternative to a high population density is to build centralized units at the edge of a living quarter or camp section where each family or group of families has access to its own latrine (preferably closed with a padlock), but this increases the distance in between the facilities and the dwellings.


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The area allowed for latrines should also be big enough to dig new pits when the first ones are full. Another possibility is to empty the full latrines. Special equipment is required however (T.B. 3.13) and the dumping site for the excreta has to be well chosen to avoid health and environmental risks and nuisances.


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The pit latrine is the most common system of excreta collection in the world. To calculate the effective volume of a pit, proceed as follows:


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The effective pit volume may be increased by 30 to 50% if bulky anal cleansing materials are used (e.g. stones, maize cobs).


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For pits that are intensively used and only have a lifetime of maximum a year, the solids accumulation rates should be doubled.


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Soils with low permeability, will have a low infiltration rate, thus filling up a lot faster than initially expected, certainly when water is used for anal cleansing.


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The effective volume represents the space available for excreta storage, but when calculating the total required pit volume, a free space with a depth of 0.5 m has to be added to the effective volume. This free space at the top of a full latrine is to avoid:


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The bottom of the pit should be at least 1.5 m above the highest possible water table, because this reduces the chance of microbiological contamination of the groundwater virtually to nil in homogeneous soils. The required vertical distance for heterogeneous soils is difficult to predict however.


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The suggested minimum lifetime of a simple family pit latrine that can’t be emptied is 5 years. Public latrines for 20 users should last for about 2 years at least before they are full. Normal twin pit latrines should have a capacity of at least 2 years per compartment in order to render the excreta completely harmless before being emptied. Ecological sanitation systems can usually do with less time to render the excreta completely harmless, if there are well operated and maintained.


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Rectangular pits can cave in rather easily, whereas circular holes have a more natural resistance against collapse because of the arching effect. Deep pits in soft sands and gravels, unconsolidated soils, (back)filled land, compressed mudstones and shale should always be lined. Soils with a significant amount of clay or high iron oxides content (e.g. laterite), or consolidated sedimentary rocks are less at risk of collapse. Nevertheless, a lining is always recommendable (in chronic emergencies and stabilized situations) for security reasons and to prolong the lifespan of a latrine.


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Rocky bottoms in which it is difficult to excavate, flood prone areas or situations with a high water table may require raised latrines (T.B. 3.12). Still, infiltration of the liquids will have to be foreseen in the underground part of these structures. Sometimes the water table is that high that contamination of the groundwater can’t be avoided. As such, it isn’t a problem to contaminate the groundwater microbiologically, as long as it isn’t used for domestic or health purposes, and/or for drinking water. It is also easier during emergencies to supply potable water than to evacuate excreta on a daily basis (except maybe if the faeces are stored in sealed plastic bags).


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It’s also important to drain runoff water away from the latrines to avoid erosion of the pit and the surroundings.


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Choose a site away from fields where crops for human consumption are grown. It should be located downwind and away from living areas (at least 30 m), avoiding watercourses and at a reasonable distance (minimum 50 m) and preferably downstream from all water sources, storage and treatment areas.


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Prepare the site: remove all debris, determine the depth of the water table and bring in the needed material and equipment.


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Fence the area (for example with plastic sheeting), and put up a zigzag entrance in order to limit the risk of animals straying and to keep as much privacy as possible (at least a strict gender separation). Additional movable screens can be placed inside the area to improve the privacy and to indicate where to defecate.


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Dig drainage channels around the defecation field fence to prevent potential runoff water from entering.


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Put a water container with a tap and soap (or ash if soap isn’t available) in an obvious place (near the exit) to allow hand washing after defecation. Make sure that an infiltration system, at least a gravel pit or preferably a soak away pit (T.B. 4.06) is foreseen.


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Provide anal cleansing material if needed, and a waste bin for sanitary towels in the women’s section.


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Allocate two trained guards (mind the gender) who should manage the correct use of the defecation field.


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Infiltration system for wastewater	- Non-transparent plastic sheeting (e.g. gravel pit)		(or local material)


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Defecation fields are not really suited during the rainy season as runoff water risks to spread the excreta, and thus the contamination over a big area. Defecation fields should also be protected against floods.


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The objective should be to replace the defecation fields as quickly as possible with a more hygienic system; e.g. improved trench latrines (T.B. 3.03), simple pit latrines (T.B. 3.04).


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Defecation fields should be clearly marked and provided with enough space; about 0.5 m²/person day (pathways not included).


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It is compulsory to build gender separated defecation fields. Simply dividing the male and female sections with plastic sheeting and providing two separate entrances may not be acceptable by the users.


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It is strongly recommended that the defecation field is utilized according to a pattern in order to use the available space most effectively. Some poles and ropes, which position has to be changed after a while, will indicate the defecation zone in use (each row maximum 20 m long, about 1.5 m wide). To encourage the full usage of a defecation zone, the guards can relocate a screen that provides some additional privacy along the row as it fills up with excreta; from the outer side of the zone towards the central alley. By using the row’s entrance also as an exit avoids that people have to pass an area that is already covered with excreta.


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When a bulldozer is available, it can be used to scrape off the ground surface at the end of the day, to be able to reuse the defecation field again. The excreta can be pushed into a trench at the edge of the field and covered with the excavated soil, to reduce the attraction of flies. In homogeneous soils, the bottom of the potential trench should be at least 1.5 m above the highest groundwater table. The required vertical distance for heterogeneous soils is difficult to predict. The water table depth can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required trench depth. When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the trench depth should be adapted accordingly. Soil saturated with water after heavy rainfall might give a false impression of the actual water table level.


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It is recommended to add wood ash every day to the excreta (within the potential trench). This gives a perceptible odour reduction. Active lime will also reduce the odours, but might slow down the decomposition of the excreta.


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If a simple infiltration system with stones and gravel is placed under the water container for hand washing, follow closely if it doesn’t clog up too fast with soil and greasy soap residues. If so, an emergency grease trap (T.B. 4.04) will have to be added.


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People could also defecate on a small pile of sand, after which they have to scoop up their excrements with a shovel and dispose of them in a drum or trench. This technique requires less space but more supervision.


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Choose a site with stable soil, downwind from living areas. It should be at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities.


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Prepare the site: remove all debris, implement a soil texture test (T.B. 4.05), determine the depth of the water table and bring in all the needed material and equipment.


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Fence the area (for example with plastic sheeting), and put up a zigzag entrance in order to limit the risk of animals straying and to keep as much privacy as possible (at least strict gender separation).


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Use string lines to lay out the trenches, 0.3 m wide (less for children) and at least 1.5 m apart from each other. Allow about 3.5 m length per 100 users.


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Dig trenches of about 0.9 m deep (1.5 m deep if a mechanical excavator is available). In unstable soils, it might be necessary to dig trenches less than 0.9 m deep (but they will fill up faster). Place the excavated soil near the side of each trench for the users to cover their excreta after each use, as to reduce the odours and the attraction of flies. Make sure there is enough space in between the trench and the excavated soil.


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Lay planks along the two sides of the trench to ensure a good foothold and to limit erosion of its edges. For safety reasons, interconnect the opposite planks with beams and anchor them to avoid that they slide away.


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Put a water container with a tap and soap (or ash if soap isn’t available) in an obvious place (near the exit) to allow people to wash their hands after defecation. Make sure that an infiltration system, at least a gravel pit or preferably a soak away pit is foreseen.


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Allocate two trained guards (mind the gender) who should manage the correct use of the trench latrines.


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underneath the planks, partly hanging in the trench  - Empty cans (to handle soil for burying excreta) (useful for trench maintenance and against erosion) - Water container (e.g. at least a 200 l drum or


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In homogeneous soils, the bottom of the trenches should be at least 1.5 m above the highest possible groundwater table. The required vertical distance for heterogeneous soils is difficult to predict however. The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required trench depth. When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the trench depth should be adapted accordingly. Soil saturated with water after heavy rainfall might give a false impression of the actual water table level.


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The planks may be replaced by wooden poles. To keep them from rolling away, dig the poles slightly in.


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It is compulsory to build gender separated trench latrines areas. Simply separating the male and female sections with plastic sheeting and providing two separate entrances may not be acceptable to the users.


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Special latrines with facilities such as a seat and handrails should be built for physically impaired people, as trench latrines can’t be used by some of them (incapable to squat). Potties are an alternative for children.


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To encourage full usage of the trenches, ropes or screens providing some privacy can indicate those in use.


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Try to make sure that the users cover their excreta with a layer of soil, located next to the trench.


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If possible, add wood ash to the trenches at least once a day. This gives a perceptible odour reduction. Active lime will also reduce the odours but might slow down the decomposition of the excreta.


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If a simple infiltration system with stones and gravel is placed under the water container for hand washing, follow closely if it doesn’t clog up too fast with soil and greasy soap residues. If so, an emergency grease trap (T.B. 4.04) will have to be installed.


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Once the trenches are nearly full (about 0.3 m from the surface), dismantle and backfill them. Don’t dig at this place again for at least two years, but plant water-absorbing trees (e.g. mangos) to re-stabilize the soil.


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The objective should be to replace the trench latrines as quickly as possible with a safer and more hygienic system; e.g. improved trench latrines (T.B. 3.03), simple pit latrines (T.B. 3.04).


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If people want to build their own facilities immediately, a shallow family trench can be an option. Apart from the size (e.g. 0.5 m x 0.3 m x 0.5 m deep), the principle is the same as for normal trench latrines.


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Choose a site with stable soil, at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities. The facilities must have an easy access, not less than 5 m and not more than 50 m away from the dwellings (< 30 m from health structure shelters).


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Prepare the site for construction: remove all debris, put up a temporary fence, implement a soil texture test (T.B. 4.05), determine the depth of the water table and bring in all the needed material and equipment.


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Lay out the trenches, using string lines. Allow per trench about 3 m length (4 slabs), for 80 - 100 users. Their width depends on the prefabricated slabs size:


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Dig a drainage channel around the improved trench latrines to lead runoff water away from the trench.


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Put plastic sheeting of at least 1 m wide on the ground along the sides of the trench. Half of its width should be laying flat on the ground (preferably up to the drainage channel to reduce the risk of erosion), where the other half should be folded so it hangs inside the trench. This plastic sheeting will ease the daily maintenance and the backfill of the improved trench latrines once full.


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Put the prefabricated (plastic) slabs down in such a way that the defecation holes are alternated in direction; 180° shifted, meaning back-to-back for small slabs and side-to-side for big slabs (as per figures) and secure them (e.g. with metal pegs).


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Put clay (or compacted earth) around the slabs to avoid direct infiltration of runoff water, rendering the trench edges unstable.


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Install vertical stakes at the corners of the slabs. By adding some horizontal sticks on top and diagonal poles at the sides, a more solid structure will be obtained. To have enough space available inside the superstructure, the vertical stakes should be about 0.15 m away from the corners of the small slabs.


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Wrap a long piece of plastic sheeting of about 2 m wide (high) around an outer corner stake, and secure it (e.g. with nails). The remaining part of the plastic sheeting has to be rolled off around the other vertical stakes in a zigzag movement (as per figure), in order that the entrances are alternated. This principle allows the rapid construction of a superstructure.


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Attach bands of plastic sheeting to the horizontal sticks of the structure to form the latrines’ curtains. Provide each curtain with horizontal sticks (bottom and middle), so that it won’t open constantly by the wind. A roof of plastic sheeting should preferably be foreseen as well, certainly in areas where it rains a lot.


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Put a water container with a tap nearby the improved trench latrines to allow hand washing after defecation. Make sure that an infiltration system (T.B. 4.06; 4.07; 4.08), preferably with a grease trap (T.B. 4.04), is foreseen.


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Provide water and soap (or ash), and anal cleansing material if required (certainly in health structures).


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Try to ensure that the cover is always replaced over the defecation hole to reduce breeding of flies and to lessen bad odours in and around the improved trench latrines’ superstructure.


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Try to have the slabs and surroundings cleaned / disinfected on a daily basis. Never put disinfectants (e.g. chlorine products) or any other chemicals in the trench as they might inhibit the natural decomposition of the faecal material. The only situation in which it is permitted to pour disinfectants or human wastes mixed with a (strong) chlorine solution into an improved trench latrine is during an epidemic of highly infectious diseases (e.g. cholera, Viral Haemorrhagic Fevers).


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Try to add wood ash into the trenches on a daily basis. This gives a perceptible odour reduction and might accelerate the elimination of pathogens. Active lime will also reduce the odours but might slow down the decomposition process of the excreta.


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Follow closely if the wastewater facilities function properly and do the necessary maintenance on the grease trap (T.B. 4.04).


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When choosing the site, ensure that buildings (e.g. health structures) and living areas are not downwind of the improved trench latrines.


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Before the trenches can be excavated, the groundwater level has to be determined. In homogeneous soils, the bottom of the trench should be at least 1.5 m above the highest possible groundwater table. The required vertical distance for heterogeneous soils is difficult to predict however. The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required trench depth. When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the trench depth should be adapted accordingly. Soil saturated with water after heavy rainfall might give a false impression of the actual water table level.


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In less stable soils, the trench will have to be lined with vertical boards (wood, corrugated iron) that are kept in place with horizontal struts. Sandbags filled with stabilised soil can also be an alternative.


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If a high water table, rocky or sandy soil prevents the excavation and use of trenches, elevated platforms may be built. It is also possible to use 200 litre drums, (partially) buried in the ground with a defecation opening at the top, or to use slabs that can be set on top of the opened drums.


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It might be necessary to build separate improved trench latrines for men and women, and foresee certainly separated facilities for the staff in health structures.


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A waste bin close to the improved trench latrines is recommended for the disposal of sanitary towels.


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In case the sanitary towels of menstruating women and girls are washed an reused, it might be appreciated if a discrete washing area with drying lines is foreseen nearby the improved trench latrines for the ladies.


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Slabs with adapted dimensions for the defecation hole and the footrests might have to be installed for small children, certainly in health structures (e.g. paediatrics ward, feeding centre, Out Patient Department). Potties, which can be emptied in the improved trench latrines, can be an alternative.


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If there are physically impaired persons amongst the population, make sure to equip some of improved trench latrines with specific features, such as a (removable) seat and handrails, because some of them will be incapable to squat (section 3.5 Further reading). Clean and disinfect these features regularly.


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Lighting at the improved trench latrines at night is highly recommended for safety / security reasons.


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Insecticide Residual Spraying (T.B. 7.15) of the plastic sheeting superstructures has potentially a high impact on the fly population.


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When the trenches are nearly full (about 0.3 m underneath the slabs), they should be dismantled and backfilled. Remove the superstructure and the slabs, and disinfect them. When the plastic sheeting of the superstructure is still in good condition, it can stay connected to the stakes, and be “replanted” around a new trench where the prefabricated slabs are already installed. Water-absorbing trees (e.g. mangos) can be planted inside the old trench to re-stabilize the underground. Before the backfilling takes place, the part of the band of plastic sheeting that is positioned on the ground can be folded towards the inside of the trench, on top of the excreta. Do not dig at the same place again for at least two years.


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If people want to build their own facilities immediately, a shallow family improved trench can be an option. Apart from the trench size (e.g. 0.5 m x 0.3 m x 0.5 m deep or 0.9 m x 0.5 m x 1.0 m deep, depending on the slab size) and the reduction in number to one slab, the principle is the same as for normal improved trench latrines.


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Choose a site at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities. The latrine (battery) must have easy access, not less than 5 m and not more than 50 m away from the dwellings (< 30 m from the buildings within a health structure).


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Prepare the site for construction: remove all debris, flatten the surface, put up a temporary fence, implement soil texture and permeability tests (T.B. 4.05), determine the depth of the water table and bring in the needed material and equipment.


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Excavate the base platform and trench, as per figure B. Keep the sides of the trench as straight as possible to obtain relatively smooth concrete surfaces afterwards.


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Prepare and install the required reinforcing bars inside the base excavation as per figure C. Make sure that the reinforcing bars stay at least 30 mm away from the sides (use spacers for the lower re-bars). Vertical reinforcement bars can be used every 2 m to keep the middle and upper re-bars in place during the casting of the concrete.


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Prepare and pour the concrete (300 kg/m³; T.B. 2.05) inside the base excavation, and vibrate the concrete to remove all the air (e.g. poke it rigorously with a reinforcing bar). Keep the concrete moist for a week with plastic sheeting or jute sacking that needs to be wetted twice a day.


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Start digging the latrine pit within the base, when its concrete has hardened for at least 3 days. Do not dig underneath the concrete base. In homogeneous loam or clay soils (T.B. 4.05), the maximum pit depth is limited to 2.5 m, and its bottom should be at least 1.5 m above the highest possible water table.


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Install perforated corrugated iron sheets vertically in the pit, overlapping each other partly, imbedded by 0.2 m in the soil, and fixed to the concrete base (as per figure A). The perforations can be done by drilling small holes or by means of a hammer and a pointed chisel.


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Install prefabricated slabs with their cover on the concrete base, once the pit is completed. To ensure a secure seating, the slabs should be fixed to its base (overlaps of at least 0.1 m) with a 10 mm thick mortar layer (T.B. 2.05). An extra anchoring with metal pegs is advised for plastic slabs.


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Construct a superstructure around the slab, adapted to local preferences. It may be built with masonry-work, wood, corrugated iron or non-transparent plastic sheeting, but preferably local materials (e.g. branches and mud) as long as this doesn’t have a too negative impact on the environment (e.g. deforestation). The superstructure should have a door if local habits dictate. A spiral-shaped superstructure without a door can also be used for a single or double latrine.


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Fit a roof to the superstructure with its slope carrying rainwater towards the back of the latrines.


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Make a drainage channel at the back and the sides of the latrines to lead the runoff water away, thus protecting the pit walls against erosion.


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Provide hand washing facilities nearby the latrines. Make sure that a grease trap (T.B. 4.04) and an infiltration system (T.B. 4.06; 4.07; 4.08) are foreseen.


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Try to ensure that the cover is always replaced on the defecation hole to reduce the breeding of flies and to lessen bad odours in and around the latrine’s superstructure.


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Try to have the slabs and surroundings cleaned / disinfected on a daily basis. Never put disinfectants (e.g. chlorine products) or any other chemicals in the pit as they might inhibit the natural decomposition of the faecal material. It is only permitted during an epidemic of highly infectious diseases (e.g. cholera, Viral Haemorrhagic Fevers) to pour disinfectants or human wastes mixed with a (strong) chlorine solution into a latrine pit.


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Add wood ash to the pit, if possible daily. This gives a perceptible odour reduction and might accelerate the elimination of pathogens. Lime also reduces the smell but might slow down the decomposition process.


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Concrete base	- Tools to prepare and pour concrete (shallow dugout and inner trench)	- Jute sacking or plastic sheeting


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Drainage channel	- Corrugated iron sheets to reinforce the pit (at the sides and back of the latrine)	- Prefabricated slab with cover


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Corrugated iron sheets	- Soap or ash, anal cleansing material (if required) (pit reinforcement)	 - Waste bin for sanitary towels (if required)


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When choosing the site, ensure that buildings (e.g. health structures) and living areas are not downwind of the latrines.


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Latrines excavated in (unstable) soils have been known to collapse, sometimes resulting in serious accidents. The construction method described above is for a latrine battery accommodating maximum six slabs. It is an assured method for all kinds of loam or clay soils (T.B. 4.05) to prevent (long) rectangular pits from subsiding. Even if the soil would cave in within the pit, the base and the slabs will stay in place, avoiding personal injuries. This design also permits a potential re-excavation of used latrines, if they have been closed for at least two years. Be aware however that the construction method described above isn’t suited for sand or loamy sand soils, due to the risk of collapse.


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An alternative for all kinds of soils is the individual circular-shaped pit, which is often more difficult to excavate but less due to collapse because of its natural arching effect. When necessary (certainly for loamy sand and sand soils), the circular pit can be reinforced with one or more concrete rings (T.B. 2.06). Another alternative is to line the rectangular pit completely (T.B. 3.07). For simple pit latrines, it isn’t necessary however to put a repartition wall between each latrine compartment. Still other valid construction methods and materials exist, but fall out of the scope of these guidelines. Contact your technical referent for more information, if needed.


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Before the pit can be dug, the depth of the groundwater table has to be determined. In homogeneous soils, the bottom of the pit should be at least 1.5 m above the highest possible groundwater table. The required vertical distance for heterogeneous soils is difficult to predict however.


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The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the maximum pit depth (2.5 m). When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the pit depth should be adapted accordingly. Soils saturated with water after heavy rainfall might give a false impression of the actual water table level.


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Allow for a spare 0.5 m of depth in the calculation of the pit size to avoid unpleasant sights and excreta splashing out during use. It also permits to cover the excreta in a safe manner when the latrine (battery) is closed down, without causing fly and odour problems. This free space is not part of the effective pit volume. A pit latrine battery constructed with the above method (max. depth of 2.5 m, thus an effective depth of only 2.0 m) will last for about 1.5 to ideally 2 years, if it is used normally by 20 people per compartment (accumulation rate of 0.06 m³/person). Similarly, a single simple pit latrine will last about 5 to 6 years for a family of 5.


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Latrines can be dug in impermeable soils (e.g. clay), but due to the low infiltration rate, they will have to be emptied frequently in a safe manner (T.B. 3.13).


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If the subsoil is very rocky, the area flood prone or the water table high, the pit needs to be constructed partially in the ground (at least 0.5 m deep) and the remaining aboveground part in a very well compacted earth mound. Hence, a specific construction technique will have to be used, as described in T.B. 3.12.


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If it rains a lot in the region, the concrete base can be made a little higher aboveground, for the pit to be less at risk of flooding. An additional mould will be needed to raise the base (foundation) by at least 0.1 m. Be aware that increasing the height of the base will necessitate a considerable amount of concrete.


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The hardening of the concrete base depends on the ambient temperature. The proposed hardening time of 3 days before the pit excavation can be started within the concrete base (whilst keeping it damp) is for temperatures of 20 °C and above. For lower temperatures, it will be necessary to wait longer.


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It is recommended to use concrete (T.B. 3.05) or plastic slabs, certainly for health structures. The use of wooden slabs should be avoided because of aging and termite problems. If used anyway, the wood quality and its impregnation (e.g. with old engine oil against termites) is important. Wooden planks have to be protected with plastic sheeting in order to make their maintenance easier. Slabs of logs should be covered with compacted soil and plastic sheeting. A regular check up of the wooden slabs and their replacement when necessary are essential safety measures.


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In case the superstructure won’t be built with masonry-work, some vertical poles can be installed before the concrete base is cast, in order to have attachments for the plastic sheeting, corrugated sheets or local material.


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Separate latrines might be needed for gender purposes. The health structure’s staff should always have their own latrines, separated from the patients’ and visitors’ facilities. Also small children might need their own adapted latrines (T.B. 3.06).


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If there are physically impaired persons amongst the population, the superstructure size of some latrines might have to be adapted. Make also sure to equip these adapted latrines with specific features, such as handrails and a (removable) seat, because some of these physically impaired people will be incapable to squat (section 3.5 Further reading). Don’t forget to clean and disinfect these specific features regularly.


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An additional non-transparent screen or wall in front of the entry side of the latrine (battery) improves the privacy, which might lead to a more frequent use of the facility.


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Make sure that correct hand washing facilities with water and soap (or ash) are provided in the direct neighbourhood of the latrines. Latrines for handicapped people (wheelchair) should be provided with washing facilities within the superstructure. Make sure that the wastewater facilities are maintained correctly.


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In some contexts, it might be interesting to integrate the latrines into sanitary blocks, together with personal hygiene facilities like (bucket) showers (T.B. 4.01). In case the women utilise reusable sanitary towels, special washing basins and drying lines could be provided in the female blocks.


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Lighting in and around of the latrines is highly recommended at night for safety / security reasons.


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Insecticide Residual Spraying (T.B. 7.15) of the interior superstructure walls (plastic sheeting included) has potentially a high impact on the fly population.


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When the latrines are nearly full (0.5 m from the slab), move the superstructure and slabs (if possible and if they are still in good condition) to a neighbouring place, after having been disinfected. The old pit can be filled with dry earth mixed with wood ash. In case the concrete base is still in a good condition, it can be re-excavated at least 2 years after the latrine (battery) has been closed. However, the corrugated iron sheets should be replaced as they will be (partly) corroded. If the latrines are demolished, water-absorbing trees (e.g. mangos) can be planted inside the filled pit to re-stabilize the underground.


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Ventilated Improved Pit (T.B. 3.07) and twin pit latrines (T.B. 3.09) can also be chosen, but they are more suited for stabilised situations, and certainly recommended for health structures.


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In the first phase of the latrines project, the recommended ratio of 1 latrine per 20 persons might not immediately be attainable, because of the time it takes to construct them.


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Make a metal or wooden mould with internal dimensions that are adapted to the slab size, and a wooden or metal template for the defecation hole.


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Cut the iron reinforcing bars to length with a hacksaw or cutting pliers and join them with metal wire (as per figure). Make 4 handles; per handle, bend a piece of re-bar in a U-shape integrating 2 pieces of pipe.


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Coat the inside of the mould and the contact surface of the template with an oily product such as used engine oil, to avoid that the concrete would stick to them.


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Place the reinforcing bars on spacers of about 2.5 - 3 cm high within the mould. Install also the 4 handles at the slab corners, making sure that their integrated pipes will be imbedded in the concrete.


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Sprinkle some cement directly on the wet concrete and polish the surface. Finalize the slab by making sloped curves around the defecation hole and footrests (useful when cleaning the slab).


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Cover the slab with plastic sheeting or jute sacking and sprinkle it twice per day with water to keep it damp during the curing period.


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Remove the mould and the template after 24 hours, recover the slab with the plastic sheeting or jute sack and keep damp.


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Wait for 7 days of curing in the shade for the concrete to gain strength, before installing the slab on the pit.


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If embarking on a programme of latrine construction, it is well worth the trouble to build a workshop for continuous slab production. This workshop should have a water point, a storage for tools and a covered area for casting and curing the slabs.


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The size of the slab has to be adapted to the pit size. However, for safety and practical reasons (slab weight), it is strongly recommended to use the slab dimensions as proposed in the figure and to adapt the pit size to the slab (T.B. 3.04). Be aware during the pit construction that the concrete slab should extend at least 10 cm beyond each side of the latrine support to ensure a secure seating.


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For a small number of slabs to be produced, the mould can also be replaced by a shallow excavation in the ground, covered with plastic sheeting. The dimensions stay the same.


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Don’t forget the handles as it is very difficult to move the slab without them. The figures suggests handles that sink into the slab once it’s installed. This reduces the risk of people tripping over them and eases the construction of the superstructure. Make sure the handles fall inside the lines indicating the overlap with the pit’s lining. Simple handles imbedded in the concrete can do as well.


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The footrests are important for the user to position himself correctly over the defecation hole (certainly at night).


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If possible, make a gentle and smooth slope over the complete slab surface towards the defecation hole; this will avoid stagnant liquids and will ease its cleaning.


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Take care of the curing (7 days in the shade, kept damp): it greatly affects the strength of the slab.


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Choose a site at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities. The latrine (battery) must have easy access, not less than 5 m and not more than 50 m away from the dwellings (< 30 m from buildings within a health structure).


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Prepare, excavate and line the pit in a similar way as described for a simple pit (T.B. 3.04) or a VIP (T.B. 3.07) latrine battery, depending on the soil type and the skills of the mason. In case the VIP latrine lining is chosen, it isn’t necessary to put a closed separation wall in between each compartment, thus it’s only required to construct the foundation circumference. The layer of lean concrete for stabilisation on the bottom of the pit is highly recommended however.


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Make slabs (T.B. 3.05 or 3.08), depending on the type of lining that has been chosen), but adapted to the size of the children: a smaller defecation hole including a matching lid, footrests that are closer together and an integrated handlebar, so that they can hold themselves in balance when they are squatting. The ventilation pipe opening in the “VIP” slabs (T.B. 3.08) isn’t needed for children’s pit latrines.


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Install the prefabricated slabs (with cover) on the latrines’ base, once it has settled for at least 3 days. To ensure a secure seating, the slab should be fixed to its base (overlaps of at least 0.1 m) with a 10 mm thick mortar layer (T.B. 2.05).


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Construct a superstructure around the slabs that is large enough for the attendants to be able to walk around the child during defecation (e.g. one open superstructure for two slabs). It may be built with masonry-work, wood or plastic sheeting, but preferably local materials (e.g. branches and mud) as long as this doesn’t have a too negative impact on the environment (e.g. deforestation). The superstructure can be open at the front in order to have more light coming in, and the child not to feel imprisoned in a rather small cubicle.


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Make a drainage channel at the back and the sides of the latrines to prevent runoff water entering the pit and creating erosion of its walls.


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Provide correct hand washing facilities in the direct neighbourhood of the latrines. Make sure that a grease trap (T.B. 4.04) and an infiltration system (T.B. 4.06; 4.07; 4.08) are foreseen.


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Try to ensure that the cover is always replaced on the defecation hole to reduce the breeding of flies and to lessen bad odours in and around the latrines’ open superstructure.


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Try to have the slabs and surroundings cleaned / disinfected on a daily basis. Don’t forget to clean and disinfect the handlebars. Never put disinfectants (e.g. chlorine products) or any other chemicals in the pit as they might inhibit the natural decomposition of the faecal material. It is only permitted during an epidemic of highly infectious diseases (e.g. cholera, Viral Haemorrhagic Fevers) to pour disinfectants or human wastes mixed with a (strong) chlorine solution into a latrine pit.


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Add wood ash to the pit, if possible daily. This gives a perceptible odour reduction and might accelerate the elimination of pathogens. Active lime will also reduce the smell but might slow down the decomposition process of the faeces.


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Defecation holes (adapted size for children)	- Fired bricks or cement blocks / 300kg/m³ with lid		concrete


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Figure shows children’s latrines on a concrete base (as per T.B. 3.04). It can also be installed on a complete lining (T.B. 3.07), depending on the soil conditions and/or the skills of the mason.


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When choosing the site, ensure that buildings (e.g. health structures) and living areas are not downwind of the children’s latrines.


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Before the pit can be dug, the groundwater table level has to be determined. In homogeneous soils, the bottom of the pit should be at least 1.5 m above the highest possible groundwater table. The required vertical distance for heterogeneous soils is difficult to predict however.


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The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required pit depth. When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the pit depth should be adapted accordingly. Soils saturated with water after heavy rainfall might give a false impression of the actual water table level.


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Allow for a spare 0.5 m of depth in the calculation of the pit size to avoid unpleasant sights and excreta splashing out during use. It also permits to cover the excreta in a safe manner when the latrine (battery) is closed down, without causing fly and odour problems. The spare space is not part of the effective pit volume. This means for instance that a pit with a maximum depth of 2 m (thus an effective depth of only 1.5 m) will only last for about 2 years if it is used normally by 20 children (accumulation rate of 0.04 m³/child).


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An alternative construction method is the individual circular-shaped pit, which is often more difficult to excavate but less due to collapse because of its natural arching effect. When necessary, the circular pit can be reinforced with one or more concrete rings (T.B. 2.06). Other valid construction methods and materials exist for (circular) latrine pits, but fall out of the scope of these guidelines. Contact your technical referent for more information, if needed.


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It is recommended to use concrete slabs (T.B. 3.05, 3.07), certainly for health structures. The use of wooden slabs should be avoided if possible because of aging and termite problems. If used anyway, the wood quality and its impregnation (with old engine oil against termites) is important. Wooden planks have to be protected with plastic sheeting to make the maintenance easier. Slabs of logs should be covered with compacted soil and plastic sheeting. A regular check up of the wooden slabs and their replacement when necessary are essential safety measures.


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In case the superstructure won’t be built with masonry-work, some vertical poles can be installed before the concrete base (T.B. 3.04) is cast, in order to have attachments for the plastic sheeting, corrugated sheets or local material.


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As the superstructure is completely open for children’s latrines, it is impossible to create some darkness inside the cubicles, and therefore the VIP fly trap principle (T.B. 3.07) won’t work. The open superstructure also results in the need for lids, so the VIP ventilation principle won’t work either, meaning that ventilation pipes aren’t necessary at all.


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If there are physically impaired children, make sure to equip some latrines with specific features, such as handrails and a (removable) seat because some of them will be incapable to squat (section 3.5 Further reading). It’s even advised to provide all children’s latrines with handles.


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When the children’s latrines are nearly full (0.5 m from the slab), move the superstructure and slabs (if possible and if they are still in good condition) to a new pit, after having been disinfected. The old pit can be filled with dry earth mixed with wood ash. In case the base is still in good state, it can be re-excavated after at least 2 years. If the latrines are demolished, water-absorbing trees (e.g. mangos) can be planted inside the pit to re-stabilize the underground.


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In the first phase of the latrines project, the aim to have a ratio of 1 latrine per 20 children might not immediately be attainable.


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Potties can (sometimes) be an acceptable alternative to children’s pit latrines. They need to be emptied and cleaned after each use.


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Determine  the  effective  pit  volume,  which  is  depending  on  the  number  of  potential  users,  the accumulation rate and the desired lifetime of the latrine (section 3.4.6). If standardised VIP slabs (T.B. 3.08) with fixed dimensions are used for a latrine battery with a certain total volume, only the required depth, including the 0.5 m needed for the free space, should be determined.


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Choose a site at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities. The VIP latrine (battery) must have easy access, not less than 5 m and not more than 50 m away from the dwellings (< 30 m from buildings within a health structure).


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Lay out the excavation area according to the outer dimensions of the foundation as per figure B, using string lines. To ease the construction works afterwards, the lay out of the excavation area can be made slightly bigger. For unconsolidated (e.g. sandy) soils, it might be necessary to dig conical walls to avoid collapse.


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Excavate the pit. The bottom of the pit should be at least 1.5 m above the highest possible water table.


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Prepare and install some reinforcing bars inside the trench system. Make sure that the reinforcing bars stay at least 30 mm away from the sides and bottom of the trench system (use spacers).


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Pour concrete (300 kg/m³; T.B. 2.05) inside the trench system to form the pit’s foundation. Vibrate the concrete to remove all the air. Keep the concrete moist for a week with plastic sheeting or jute sacking that needs to be wetted twice a day.


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Build on top of the foundation, which has hardened for at least 3 days, the open-jointed (honeycombed) lining and the sealed (closed) partition walls that divide the pit into different compartments (as per figure C). The lining and partition walls, erected in cement blocks or a double layer of fired bricks, should overlap correctly in all the corners (as per figure D) to be able to resist the ground pressure.


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Build a sealed lining with cement blocks or a double layer of fired bricks on top of the open-jointed lining and partition walls.


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Prepare and install every 0.2 m the required reinforcing bars inside the casing (as per figure E). Make sure that the reinforcing bars stay at least 25 mm away from the sides of the casing (use spacers).


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Pour the concrete (300 kg/m³) inside the casing, while tapping gently on its sides. The concrete can also be vibrated by poking it with a reinforcing bar. Keep the concrete moist for a week to ensure correct curing.


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Pour a layer of lean concrete (150 kg/m³; T.B. 2.05) at the bottom of the pit. It will give extra support to the lining. Keep this concrete moist and cover the whole pit with plastic sheeting.


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Install prefabricated VIP slabs (T.B. 3.08) on the ring beam that has hardened for at least 3 days. To ensure a secure seating, every slab should have a good overlap over its entire circumference with the lining and partition walls (respectively 0.15 and 0.075 m) and be fixed with a 10 mm thick mortar layer.


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Backfill the space in between the pit lining and the excavated hole with gravel (honeycombed part) and compacted soil (sealed part and concrete ring beam).


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Construct a superstructure on top of the slabs, adapted to local preferences. It may be built with masonry-work, wood or local materials. Plastic sheeting is not appropriate as it might not provide enough darkness for the VIP principle to work (flies being attracted by light only entering via the vent pipe).


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Fix a plastic ventilation pipe with a diameter of 150 mm to each slab and secure it to the superstructure. Put some mortar around the pipes where they pass through the roof.


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Fit corrosion / UV-resistant screens at the pipes’ top and above the doors to avoid the entry and exit of flies.


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Ventilation pipe	- Jute sacking or plastic sheeting (internal size depending on material used)	- Fired bricks or cement blocks


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Intermediate reinforced concrete ring beam	- Waste bin for sanitary towels (if required) (depending on the height of the lining (> 3 m deep)


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Air and light inlet covered with mosquito netting	n: number of slabs (max. 6) (only one, area = at least 3 times the vent section)	b: width of a slab


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Do not use a cover on the defecation hole of a VIP latrine as this would stop the air circulation needed for the ventilation.


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Try to have the slabs and surroundings cleaned on a daily basis. Never put disinfectants (e.g. chlorine products) or any other chemicals in the pits as they might inhibit the natural decomposition of the faecal material. It is only permitted during an epidemic of highly infectious diseases (e.g. cholera, Viral Haemorrhagic Fevers) to pour disinfectants or human wastes mixed with a (strong) chlorine solution into a latrine pit.


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Add wood ash to the pit, if possible daily. This reduces the odours even more and might accelerate the elimination of pathogens. Lime also reduces the smell but might slow down the decomposition process.


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Pour once in a while a bucket of water through the vent pipes to remove spider webs and flies corpses that could block the ventilation. Check also if the screens on top of the ventilation pipes and above the doors are still intact and replace them when necessary.


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When choosing the site, ensure that buildings (e.g. health structures) and living areas are not downwind of the VIP latrines. VIP latrines should also be built on an open space, away from trees, buildings or other objects that could impede air movement.


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Latrines excavated in (unstable) soils have been known to collapse, sometimes resulting in serious accidents. The construction method described above is for latrine batteries accommodating up to 6 standard VIP slabs (T.B. 3.08), with a maximum pit depth of 3 m. It is an assured method for all kinds of soils to prevent (long) rectangular pits from collapsing. For pits exceeding 3 m depth, it is recommended to cast an intermediate ring beam halfway the height of the lining.


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Allow for a spare 0.5 m of depth in the calculation of the pit size to avoid unpleasant sights and excreta splashing out during use. It also permits to cover the excreta in a safe manner when the latrine (battery) is closed down, without causing fly and odour problems. This free space is not part of the effective pit volume.


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The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required depth. When pulled out, the rod or (the earth inside) the pipe should be dry. If not, the pit depth should be adapted accordingly. Soils saturated with water after heavy rainfall might give a false impression of the actual water table level.


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Single VIP latrines can also be build with the method described above. An alternative is the individual circular-shaped pit, which is often more difficult to excavate but less due to collapse because of its natural arching effect. When necessary, the circular pit could be reinforced with one or more concrete rings (T.B. 2.06). Still other valid construction methods and materials exist, but fall out of the scope of these guidelines. Contact your technical referent for more information, if needed.


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VIP latrines can be dug in impermeable soils (e.g. clay), but due to the low infiltration rate, they will have to be emptied frequently in a safe manner (T.B. 3.13).


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In case the soil is unstable, the pit will need to be supported with struts during the works or be excavated conically.


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If the subsoil is very rocky, the area flood prone or the water table high, the method described above can be adapted with the pit partially constructed underground (at least 0.5 m deep) and the remaining aboveground part in a very well compacted earth mound (T.B. 3.12).


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The hardening of the concrete elements depends on the ambient temperature. The proposed hardening time of 3 days before the construction can continue on the concrete elements (whilst keeping them damp) is for temperatures of 20 °C and above. For lower temperatures, it will be necessary to wait longer.


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The door of a VIP superstructure should be self-closing. Above each door should be an air hole for ventilation purposes. This air hole should have a surface at least three times larger than the cross sectional area of the ventilation pipe, and be covered with a screen (mosquito netting).


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If it is acceptable to the population, the superstructure of a single or double VIP latrine can also be made in a spiral form without a door. This still provides enough darkness inside for the VIP principle to work.


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The separation in individual compartments by solid walls going from the bottom until the top of the pit is needed to avoid shortcuts of the air movement between the different defecation holes, which would hamper the VIP ventilation principle. This means as well that every single compartment of the VIP latrine battery should have its own ventilation pipe.


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Each ventilation pipe should be vertical, sticking out above the latrine’s roof by at least 0.5 m (as per figure A). The hole where the vent pipe comes through the roof should be made watertight to avoid leaks. The pipe should also be flush with the slab’s underside. To ensure a better anchorage of the plastic vent pipe at the bottom, a clamp can be connected at the level where it will be mortared in the slab. An alternative is to provide the VIP latrine slab already with a short piece of pipe (spigot), being anchored in the concrete. It should be flush with the underside of the slab and sticking out above by at least 0.1 m. Once the slab is installed, the vent pipe can be slit over the spigot. This spigot facilitates the construction, but makes the transport of the slab more difficult (without breaking the spigot).


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mm. Having a dark coloured plastic vent pipe at the outside of the superstructure and oriented towards the sun might allow a better ventilation of the VIP latrine during wind still days, but complicates the construction.


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Instead of a round plastic vent pipe, local alternatives such as reeds or bricks covered with earth plaster have been used already as well. When bricks are used for the vent pipe, its form will be square with internal dimensions of at least 225 mm x 225 mm, because their rougher surface (still preferably plastered) hinders the airflow. The size of the hole in the latrine slab should be adapted accordingly.


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The fly screen on the top of the vent pipe must be in stainless steel, aluminium or PVC coated fibreglass, because the gasses escaping from the latrine are very corrosive to mild metal. Stainless steel seems to be the best but also the most expensive material for the screen, while aluminium seems to be the best quality/prize option. If really nothing else is available, painted metal mesh is the last option.


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Separate VIP latrines might be needed for gender purposes. The health structure’s staff should always have their own latrines, separated from the patients’ and visitors’ latrines. VIP latrines are not really suited for small children; therefore special children’s latrines might have to be built (T.B. 3.06).


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If there are physically impaired persons, the size of the superstructure of some VIP latrines might have to be adapted. Make also sure to equip these adapted VIP latrines with specific features, such as handrails and a (removable) seat, because some of these physically impaired people will be incapable of squatting (section 3.5 Further reading). Don’t forget to clean and disinfect these specific features regularly.


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An additional non-transparent screen or wall in front of the entry side of the VIP latrine (battery) improves the privacy, which might lead to a more frequent use of the facility. However, this screen / wall should not impede the air circulation needed for the VIP principle to work.


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Make sure that correct hand washing facilities with water and soap (or ash) are provided in the direct neighbourhood of the VIP latrines. VIP latrines for handicapped people (wheelchair) should be provided with washing facilities within the superstructure. Make sure that the wastewater facilities are maintained correctly.


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In some contexts, it might also be interesting to integrate the VIP latrines into sanitary blocks, together with personal hygiene facilities like (bucket) showers (T.B. 4.01). In case the women utilise reusable sanitary towels, special washing basins with drying lines could be provided in the female blocks.


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Insecticide Residual Spraying (T.B. 7.15) of the VIP latrines’ interior superstructure walls has potentially a high impact on the fly population.


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When the pit is nearly full (0.5 m from the slab), close it down by filling the pit with dry earth mixed with wood ash. Since VIP latrines demand a considerable investment, it should be checked first if they can be emptied in a correct way (T.B. 3.13). With the complete lining, the pit is less at risk of collapse, so water can be added to render the sludge more liquid. However, do not empty VIP latrines manually for at least two years. Twin pit latrines (T.B. 3.09) could be considered as an alternative. If the VIP latrines are demolished, water absorbing trees (e.g. mangos) can be planted in the pit to re-stabilize the underground.


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Make a metal or wooden mould with internal dimensions that are adapted to the slab size, and wooden or metal templates for the defecation and ventilation pipe holes.


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Coat the inside of the mould and the contact surface of the templates with an oily product such as used engine oil, to avoid that the concrete would stick to them.


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Place the reinforcing bars on spacers of 2.5 - 3 cm high within the mould. Install also the 4 handles at the slab corners, making sure that their integrated pipes will be imbedded in the concrete.


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Sprinkle some cement directly on the wet concrete and polish the surface, and finalize the slab by making sloped curves around the defecation hole and footrests (useful when cleaning the slab).


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Remove the mould and the templates after 24 hours, recover the slab with the plastic sheeting or jute sack and keep damp.


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Wait for 7 days of curing in the shade for the concrete to gain strength before installing the slab on the pit.


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If embarking on a programme of latrines’ construction, it is well worth the trouble to build a workshop for continuous slab production. This workshop should have a water point, a storage for tools and a covered area for casting and curing the slabs.


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The size of the slab has to be adapted to the pit size. However, for safety and practical reasons (slab weight), it is strongly recommended to use the slab dimensions as proposed in the figure and to adapt the size of the pit accordingly (T.B. 3.07). Be aware that the slab should extend 15 cm beyond each side of the lining to ensure a secure seating. When several VIP slabs are positioned next to each other, they should rest correctly on the pit’s repartition walls by at least 7.5 cm. The slabs should be mortared to their supporting walls to avoid air movement shortcuts between the defecation holes and to deny access to flies and other vectors.


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Don’t forget the handles. It is very difficult to move the slab without them. The figures suggests handles that sink into the slab once it’s installed. This reduces the risk of people tripping over them and eases the construction of the superstructure. Make sure the handles fall inside the lines indicating the overlap with the pit’s lining. Simple handles imbedded in the concrete can do as well.


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Don’t forget the hole for the ventilation pipe (preferably a diameter of 15 cm for plastic pipes), as far away as possible from the defecation hole (at least 30 cm), but free from the sides where the slab will be seated on the supporting pit walls. An alternative is to integrate immediately a spigot (plastic pipe sticking out by at least 0.1 m on top of the slab, but flush with its underside) on which the vent pipe will be installed later.


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The templates for the defecation and the ventilation pipe holes should be tapered to ease their withdrawal from the concrete.


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The footrests are vital for the user to position himself correctly over the defecation hole (certainly at night).


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If the slab is used for children’s latrines, the dimensions of the drop hole and the footrests must be adapted (T.B. 3.06), and the vent pipe hole isn’t necessary, because the VIP principle won’t work anyway with the open superstructure.


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The construction of a twin pit latrine is very similar to a VIP latrine battery (T.B. 3.07) with two compartments, but its design has some specific features, as described below:


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To permit easy access to each pit during the emptying procedure, their dimensions have to be adapted. The suggested outer dimensions for the lining of the complete twin pit latrine are 2.4 m x


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2.0 m, if this would permit to have the bottom of the pit still 1.5 m above the highest possible water table (taking into account the accumulation rate and the free space of 0.5 m for backfilling; section 3.4.6). For these lining measurements, the outer dimensions of the foundation should be 2.55 m x


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Standard size slabs (T.B. 3.05) can be used if the ventilation pipe is located outside the superstructure. An alternative is to cast a big slab in situ over the whole area where the superstructure will be constructed.


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Per twin pit latrine, 8 small reinforced concrete slabs should be cast (for the suggested lining dimensions: each slab should be 1.0 m x 0.3 m):


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➞ 2 slabs with a ventilation hole according to the available vent pipe (ideally a PVC pipe with a diameter of 150 mm, or at least 110 mm).


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➞ The ventilation pipes will have to be anchored to the outside of the superstructure to avoid being blown over by heavy winds. A dark colour of the ventilation pipes will help the airflow during wind still days, if the pipes are oriented towards the sun.


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After a period of at least 2 years, the first pit will be full (filled to 0.5 m underneath the slab):


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After a further period of at least two years, the second pit will be full (filled to 0.5 m under the slab):


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In this way, the alternation between pits may be repeated indefinitely until the latrine is completely worn out. The material taken out is inoffensive and is an excellent soil conditioner, with some fertilizing capacity.


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Drainage channel	- PVC pipes (preferable diameter of 150 mm) (at the sides and back of the latrine)	- Screen (e.g. mosquito netting)


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Air and light inlet covered with mosquito netting	Measurements are indicated in m (only one, area = at least 3 times the vent section)	 Drawings not up to scale


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Before considering the construction of twin pit latrines, it is important to know if this technique is acceptable for the population as it implies handling of “faecal” material during pit emptying (even if the material doesn’t resemble excreta anymore, nor is it harmful to health). Social, religious and/or cultural factors may forbid it and demand the use of another method for excreta disposal.


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The correct size of each pit is essential: each one should permit the storage of faecal and anal cleansing material for at least 2 years, during which all possible pathogens are certainly eliminated (biodegradation).


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When access for physically impaired persons is required, the dimensions of the superstructure will most probably have to be increased, implying that the pit will have to bigger as well.


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The defecation hole that isn’t in use should be covered with a lid that can’t be removed easily (e.g. mortared). However, do not put a lid on the defecation hole of the pit in use as this prevents the air circulation and thus the VIP principle to work.


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Installing only one door per twin pit superstructure reduces the risk that both defecation holes would be opened and used at the same time, which would render their safe emptying process impossible.


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The use and regular maintenance of a twin pit latrine are very similar to a normal VIP latrine (T.B. 3.07), thus the related issues (e.g. gender separation, principle not suited for small children) and the facilities (e.g. handle bars and movable seat for physically impaired people, hand washing facilities, light outside latrine) are comparable as well.


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It is possible to transform a twin pit latrine into a real ecological sanitation (Eco-San) latrine by separating the urine from the faecal matter and stirring its content regularly (section 3.5 Further reading).


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Adding regularly wood ash, some green organic waste and vegetables can help already to reduce bad odours and potentially enhance the elimination of pathogens.


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After a minimum of two years for normal twin pit latrines (potentially less for Eco-San latrines), the “compost” may be taken out and be used as soil conditioner.


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The emptying process is a good moment to do a complete check-up of the twin pit latrine. Any damages should be repaired, in order to guarantee / increase the lifespan of the twin pit latrine.


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Remember to provide protective clothing and washing facilities (at least water and soap) to the workers emptying the pits.


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Risk of blockages when solid materials (e.g. maize cobs, stones) are used for anal cleansing. Also sanitary towels shouldn’t be discarded in a pour-flush latrine.


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Hence, opting for pour-flush latrines should be a rational choice; e.g. because the population is already accustomed with this system and/or latrines have to be available inside a building.


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The chosen excreta evacuation system of a pour-flush latrine will have an influence on its location, design and construction steps:


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This onset pour-flush latrine with its slab directly on top of the pit (figure A) is the simplest method. It is obligatory that the pit has an open-jointed lining until the bottom because the amounts of water used for flushing (and anal cleansing) might render the soil unstable and collapse.


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The location and construction steps are similar to those described for the VIP latrine (T.B. 3.07), but the VIP slab is replaced by a model fitted with a water pan and water-seal. A pour-flush latrine battery doesn’t need the sealed partition walls inside the pit as a VIP latrine, but it certainly requires the stabilisation layer in lean concrete (150 kg/m³) at the bottom of the pit to avoid implosion.


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Intermediate reinforced concrete ring beam	- Water supply with tap and evacuation system (300 kg/m³; optional, depending	 - Soap or ash


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The water-seal is connected via a pipe to a (double) offset pit, thus the water pan can be located within a building or an independent superstructure. The offset location also makes it easier to empty the pits when nearly full. Two offset pits with open-jointed lining put in parallel, each with an accumulation capacity for at least 2 years, permit a safe long-term alternating use of the system.


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Be aware that a minimum distance of 6 m between the pits and the dwellings / building foundations must be respected. The pits must be at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities.


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For soils with a good infiltration rate (T.B. 4.05), round pits that are lined with perforated concrete rings (T.B. 2.06) can be constructed. When alternating pits are installed, they should be at least 1.5 m from each other.


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For soils with a low infiltration rate (T.B. 4.05), large pits will be needed. Hence, the lined pits can be constructed following the steps as described for VIP latrines (T.B. 3.07), with adapted dimensions. The sealed partition walls aren’t required, but the lean concrete stabilisation layer at the bottom is strongly recommended however. The VIP slabs need to be replaced by plain concrete slabs. It is advisable to install small slabs with handles (e.g. 0.3 m wide) side-by-side to be able to remove them more easily when the pit needs to be emptied (weight reasons). To avoid bad odours and to deny access to vectors and other animals, the slabs should be mortared to the pit lining.


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A shallow pit, with a foundation at the bottom and closed walls on top that are backfilled, form the support for the slab that integrates the water pan with water-seal.


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The water-seal is connected via a pipe to the septic tank (figure B), thus the water pan can be located within a building or an independent superstructure. The septic tank is attached to an infiltration system (T.B. 4.06; 4.07) or a closed sewer, if existent. When pour-flush latrines are used, the septic tank is certainly the preferred option for health structures, but they have to be designed and constructed by skilled people.


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The location, design and construction of a septic tank are described in T.B. 3.11. A minimum distance of 6 m between the septic tank and the dwellings / building foundations should preferably be respected.


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A shallow pit, with a foundation at the bottom and closed walls on top that are backfilled form the support for the slab that integrates the water pan with water-seal.


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➞ Provide water containers with a suited volume to perform the flushing. Be aware that the amount of water needed per flush depends on the diameter of the water-seal: as a rule-of-thumb; a 90 mm diameter requires 2 – 3 l to flush effectively, whereas 4 – 5 l will be needed for a 120 mm diameter.


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Verify if the users have a water container for anal cleansing. If not, the size of the flushing container can be adapted or specific anal cleansing containers can be made available. Alternatives are to provide soft anal cleansing material that can be flushed (e.g. toilet paper), or that every cubicle is foreseen with a waste bin in which solid anal cleansing material can be deposited. These bins could potentially also be used to discard single use anal cleansing containers (e.g. plastic bottles) and sanitary towels.


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Try to have the slabs with water pan and the surroundings cleaned on a daily basis. Never pour disinfectants (e.g. chlorine products) or any other chemicals in the pour-flush latrines as they might inhibit the natural decomposition of the faecal material. It is only permitted during an epidemic of highly infectious diseases (e.g. cholera, Viral Haemorrhagic Fevers) to pour disinfectants or human wastes mixed with a (strong) chlorine solution into a pour-flush latrine.


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Check the pour-flush latrines frequently; if these toilets block they should be cleared quickly. Otherwise the material blocking the latrine will solidify and plug the water-seal. Never allow the pit to fill above the water-seal (siphon) level as it will clog up the whole system.


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As a general rule, the pour-flush latrine is mainly suitable for regions where water is abundant and habitually used for anal cleansing. In other cases, it is better to use dry pit latrines (T.B. 3.04), preferably VIP types (T.B. 3.07) for public buildings or even twin pit latrines (T.B. 3.09) if the removal of the residues is socio-culturally acceptable.


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Pour-flush latrines should be avoided in impermeable soils (e.g. clay) due to the very low infiltration rate.


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Allow for a spare 0.5 m of depth in the calculation of the pit size to cover the excreta in a safe manner when the pour-flush latrine (battery) is closed down, without causing fly and odour problems. The free space is not part of the effective pit volume.


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In places where (pour-)flush systems are commonly used, prefabricated pans (porcelain, plastic, smoothed cement) can often be found, but they are also available as emergency equipment. Verify that the water-seal has a minimum diameter of 75 mm, otherwise the risk of blockages is very high.


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The slope of the pipe behind the water-seal should be at least 2.5%, but 5% would be better. In case the distance in between the water-seal and the pit / septic tank is more than 2 m, a manhole should be foreseen in the middle to allow the pipe to be unclogged.


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Separate pour-flush latrines might be needed for gender purposes. The health structure’s staff should always have their own latrines, separated from the patients’ and visitors’ facilities. Also small children might need their own adapted latrines.


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If there are physically impaired persons amongst the population, the size of the superstructure of some pour-flush latrines might have to be adapted. Make also sure to equip these adapted latrines with specific features, such as handrails and a (removable) seat, because some of these physically impaired people will be incapable to squat (section 3.5 Further reading). Don’t forget to clean and disinfect these specific features regularly.


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It is essential to have a water point nearby so that the users can take water to flush the latrine after each use. If the water supply would (partly) fail, closure of these latrines and (temporary) replacement by a system not using water should be considered.


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These water points could also be used for hand washing, thus soap or ash should be available. Pour-flush latrines for handicapped people (wheelchair) should be provided with washing facilities within the superstructure. Make sure that the wastewater facilities are maintained correctly.


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It might be needed to install a refuse collection system nearby the pour-flush latrines to avoid users discarding their solid anal cleansing material, their anal cleansing container (e.g. old mineral water bottle) or their used sanitary towels in the water pan itself, thus blocking the whole system.


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In some contexts, it might be interesting to integrate the pour-flush latrines into sanitary blocks, together with personal hygiene facilities like (bucket) showers (T.B. 4.01). In case the women utilise reusable sanitary towels, special washing basins with drying lines could be provided in the female blocks.


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Insecticide Residual Spraying (T.B. 7.15) of the interior superstructure walls (plastic sheeting included) has potentially an important impact on the fly population.


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When the pit is nearly full (0.5 m underneath the slab), close it down by filling the pit with soil. Since pour-flush latrines demand a considerable investment, it should be checked first if they can be emptied in a correct way (T.B. 3.13). With the lining, the pit is less at risk of collapse, so plenty of water can be added to render the sludge more liquid. However, do not empty the pit manually for at least two years. If the pour-flush latrines are demolished, water absorbing trees (e.g. mangos) can be planted in their pit to re-stabilize the underground. A septic tank can be emptied over and over again, but it has to be done in a safe manner (T.B. 3.13).


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When pour-flush latrines are required in acute emergencies, individual circular-shaped pits are recommended. Their lining can be made with perforated concrete rings (T.B. 2.06) or drums. A prefabricated (plastic) slab with water-seal (module) will have to be put on top of each lining and be anchored with pegs in the soil.


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A septic tank is a container, often rectangular in shape, built just underground, in which wastewater is retained for 1 to preferably 3 days. During this period, the solid material settles. Over time, the faecal material will be decomposed by an anaerobic bacteriological process, which reduces the volume of the sludge. Although this biodegradation is reasonably active (depending on the temperature), the sludge does accumulate, which means that the tank needs emptying at regular intervals, generally every 1 to 5 years.


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The effluent from the tank is still contaminated by pathogens, thus it cannot be released directly in the open environment. Therefore, dispersal in the underground, preferably via infiltration trenches (T.B. 4.07) is essential to benefit from the natural filtration process. In places where infiltration trenches wouldn’t work because of the limited soil permeability, a filtration system will have to be installed before the effluent can be disposed of into a river or a stream. A perfect alternative might be a correct and closed sewerage system, if it would be already available at the site.


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Although a septic tank is constructed in a similar way as a grease trap (T.B. 4.04), it has its own important design features, as following:


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In order to reduce the concentration of suspended material in the effluent, the tank is divided into two interconnected compartments, the first having double the volume of the second. The effective depth of the liquid zone is 1.2 to 1.7 m. The total length of the tank is usually 2 to 3 times its width.


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The volume of the septic tank is calculated on the basis of a 3 days retention time of the quantity of water entering each day.


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The septic tank should be emptied frequently; a simplified estimation is when it is 1/3 full of sludge. The frequency is thus given by:


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Veff = effective volume of the septic tank; volume of the tank that can be filled in m³ S = sludge accumulation rate in m³/person year


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The sludge accumulation depends on the temperature, but a figure of 0.025 – 0.03 m³ per person a year can be considered sufficient as estimation, if only sewage passes through the septic tank. After emptying the septic tank, it is necessary to refill it with water. Some of the old sludge can also be poured into the tank, to accelerate the growth of decomposing bacteria.


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A health structure with 4 pour-flush latrines; according to the Essential Requirements (T.B. 1.08): 20 users each.


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It is not recommended for health structures to combine the degreasing of sullage (grey water) with the pre-treatment of sewage (black water) by passing both through the same septic tank. To cope with the considerable volumes of sullage generated in health structures, the required capacity of their septic tanks might be very important in order to respect the minimum retention time for the sewage (1 to preferably 3 days). Grease traps (T.B. 4.04) are definitely a better option for grey water as their minimum effective volume should only be double the maximum hourly flow entering the trap.


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The location of the septic tank is dictated by the position of the dispersal area (e.g. infiltration trenches, T.B. 4.07), but it should also be nearby the buildings that it is serving. The tank should be away from vehicular passage, but accessible for maintenance however.


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Make sure there is enough land available for the underground dispersal system and that the soil allows a sufficient infiltration rate (T.B. 4.05).


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If the water table is not deep enough (should be at least 2 m deep) or the soil isn’t very absorbing, do contact your technical referent for further advice.


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A septic tank may be built in situ in concrete or masonry-work (e.g. cement blocks) and made watertight with plastering mortar (T.B. 2.05), or alternatively with prefabricated panels or a complete tank of concrete, fibreglass or plastic. If built in situ, the construction steps as described for the grease trap (T.B. 4.04) can be followed, taking in consideration the specific dimensions and ratios of a septic tank.


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Whatever the construction method, the tank must be watertight and strong enough to resist to soil and possible groundwater pressures. It should rest on a sub-base of sand several centimetres thick.


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The covers of the septic tank should be at least 0.1 m above ground level to avoid infiltration of surface water (e.g. rainwater).


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The minimum diameter of the inlet and outlet pipes with their respective T-piece should be at least 100 mm, and their slope at least 2.5%, although 5% is preferable.


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The gasses resulting from anaerobic decomposition in the septic tank should be evacuated by a ventilation pipe with a minimum diameter of 100 mm (preferably 150 mm, if available). The pipe should be installed at such a place and such a height that there is no odour nuisance (take into account the dominant wind direction). It is preferably located directly on top of the septic tank, if possible. The outlet of the ventilation pipe must have a stainless steel, aluminium, PVC coated fibreglass or even a nylon screen to avoid vectors entering. Regular checks of this screen are strongly recommended, and it should be replaced when it is not longer intact.


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Chlorine products and detergents used for a health structure’s normal maintenance and cleaning will not affect the tank’s functioning (bacterial activity). However, high dosages of disinfectants or any other chemicals should not be evacuated via the septic tank as they might inhibit the natural decomposition of the faecal material.


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It is not necessary to use special additives in the septic tank to be re-activated after it has been emptied. Some of the old sludge could be added to accelerate the growth of decomposing bacteria, but generally the new faecal material collected in the septic tank is rich enough in micro-organisms to start the biodegradation.


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Septic tanks should be inspected regularly; once every 6 months for public buildings and health structures.


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Determine the effective pit volume, which is depending on the number of potential users, the accumulation rate and the desired lifetime of the latrine (section 3.4.6).


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Choose a site at least 30 m away (more for fissured underground and limestone) and downhill from all water sources, storage and treatment facilities. The latrine (battery) must have easy access, not less than 5 m and not more than 50 m away from the dwellings (< 30m from buildings within a health structure).


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Prepare the site for construction: remove all debris, flatten the surface, put up a temporary fence, implement soil texture and permeability tests (T.B. 4.05), and determine the depth of the water table. The depth of the water table can be estimated by verifying the water level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, at least 2 m beneath the ground surface. When pulled out, the rod or (the earth inside) the pipe should be dry. Soil saturated with water after heavy rainfall might give a false impression of the actual water table level.


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Decide on the maximum depth of the underground part, with respect for the minimum required vertical distance of 1.5 m between the bottom of the pit and the highest possible water table. As such, in order to leave an additional 0.5 m depth available for the infiltration of liquids, the highest possible water table should be at least 2 m deep for homogeneous soils. The required vertical distance for heterogeneous soils is difficult to predict however.


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Calculate the remaining height needed for the aboveground part (receiving slabs with standard dimensions) to obtain the desired total volume, including the 0.5 m required for the free space. In case the height of the aboveground part would surpass 2 m, non-standardised concrete slabs with a bigger size can be used, but be aware of the weight increase this will imply.


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Lay out, using string lines, the excavation area according to the outer dimensions of the foundation (as per figure B, or a bigger surface if non-standardised slabs or a raised twin pit latrine are desired).


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Prepare and install some reinforcing bars inside the trench. Make sure that the reinforcing bars stay at least 30 mm away from the sides and bottom of the trench (use spacers).


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Build on top of the foundation, which has hardened for at least 3 days, the open-jointed (honeycombed) lining and the sealed (closed) partition walls that divide the pit into different compartments (as per figure C). The lining and partition walls, erected in cement blocks or a double layer of fired bricks until approximately 0.1 m underneath the ground surface, should overlap correctly in all the corners (as per figure D) to be able to resist the ground pressure.


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Arrange on top of the lining and the partition walls the casing for the intermediate concrete ring beam.


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Pour a layer of lean concrete (150 kg/m³; T.B. 2.05) at the bottom of the pit. It will give extra support to the lining. Keep this concrete moist for a week and cover the whole pit with plastic sheeting.


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Backfill the space in between the pit lining and the excavated hole with gravel (honeycombed part) and compacted soil (intermediate concrete ring beam).


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Build on top of the intermediate ring beam that has hardened for at least 3 days the sealed lining and partition walls to a height of maximum 2 m. The lining and partition walls, built with cement blocks or a double layer of fired bricks, should overlap correctly in all the corners.


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Build a compacted earth mound around the whole construction. This can be done in several soil layers, each one watered and rolled to be compacted. The mound slope depends on the stability of the soil used. At the top of the earth mound, it is advisable to foresee a little platform around the structure for safety reasons. Plant in a later stage some grass on the mound to reduce its erosion.


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Install prefabricated slabs (T.B. 3.08) on the upper ring beam after it has hardened for at least 3 days. To ensure a secure seating, every slab should have a good overlap over its entire circumference with the lining and partition walls (respectively 0.15 and 0.075 m) and be fixed with a 10 mm thick mortar layer (T.B. 2.05).


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Construct the superstructure with its potential accessories, keeping local preferences in mind. As a raised latrine is an important investment, it’s recommended to make the superstructure also in durable materials. The superstructure should have a door.


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Fit a roof to the superstructure with its slope carrying rainwater towards the back of the latrine (battery).


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Make a drainage channel at the back and the sides of the latrine (battery) to lead the runoff water down and away, thus protecting the whole construction against erosion.


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Build an access ramp (for impaired persons) and/or a stairway in concrete or masonry-work on the earth mound to allow easy access to the latrine (battery). A handrail is strongly recommended because the access can get slippery when wet.


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Ventilation pipe	 - Fired bricks or cement blocks (internal size depending on the material used)	- Prefabricated slabs


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Fly screen	- Material and tools for the superstructure (corrosion and UV-resistant material)	- PVC pipe (diameter of 150 mm), screen


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Air and light inlet covered with mosquito netting	b: width of a slab (only one, area = at least 3 times vent section)


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When choosing the site, ensure that buildings (e.g. health structures) and living areas are not downwind of the raised pit latrines. If the VIP model is chosen, it should be built on an open space, away from trees, buildings or other objects that could impede air movement.


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The construction method described is for raised pit latrine batteries of up to 6 standard slabs. As a raised pit latrine is a considerable investment, there is a tendency to make it more as a VIP model (as per figure A) or even as a twin pit model. The special features for these models are described in T.B. 3.07 and 3.09.


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Single (simple) raised pit latrines can be build as well with this method. An alternative is the individual circular-shaped raised pit latrine. This can be made by installing perforated concrete rings underground, and plain concrete rings (T.B. 2.06) aboveground within a compacted earth mound. The rings should be cemented and preferably bolted together to be watertight.


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Be aware that the infiltration rate of a raised pit latrine can be low, certainly when the permeable part of the lining is limited in size. This could mean that the pit will have to be emptied on a regular basis (T.B. 3.13), certainly when water is used for anal cleansing. As such, raised pit latrines should preferably not be made with a pour-flush system as lots of water will be introduced (T.B. 3.10).


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In case the water table level is less than 2 m deep, the normal construction of raised latrines with earth mound won’t be sufficient to avoid microbiological contamination of the groundwater. Following options are possible under these circumstances:


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➞ Make a pit with its bottom close to or even within the aquifer, which will result in contaminated groundwater. But it is usually easier and cheaper to develop onsite sanitation and find an alternative solution for the water supply (e.g. during emergencies, it is easier to supply potable water than to evacuate excreta on a daily basis). However, an in-depth assessment is required before the construction of the latrines begins, to make sure that the groundwater is not exploited for human consumption at present, nor will be in the near future.


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➞ Install an impermeable reservoir, partly underground in a pit (even within the aquifer) and partly aboveground in an earth mound, and closed on top with latrine slabs. This impermeable reservoir can for instance be a large (round) plastic or fibreglass water storage tank, weighted down so it doesn’t float if it would be located inside the aquifer. This avoids groundwater contamination, but the tank will often have to be emptied in a safe manner (T.B. 3.13). The solution of an impermeable reservoir can also be interesting for excreta disposal facilities that have to be constructed on rocky grounds.


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In case of very permeable or fissured soil, the risk of microbiological contamination of the groundwater can potentially be reduced by making the excavation a lot bigger (e.g. 1 m on all sides,) and by backfilling the gap between the hole walls and the permeable lining with fine sand, topped up with compacted soil at the level of the sealed lining. The sand layer will filter the pathogens out to a certain extent, which will reduce, but not completely avoid the contamination of the groundwater.


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In case the underground soil is too unstable, the pit will need to be supported with struts or be made conical.


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Allow for a spare 0.5 m of depth in the calculation of the pit size to avoid unpleasant sights and excreta splashing out during use. It also permits to cover the excreta in a safe manner when the latrine is closed down, without causing fly and odour problems. The spare space is not part of the effective pit volume.


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Separate raised pit latrines might be needed for gender purposes. The health structure’s staff should always have their own latrines, separated from the patients’ and visitors’ latrines. Special facilities or potties might be needed for children as well.


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If there are physically impaired persons, the size of the superstructure might have to be adapted. Make also sure to equip the adapted latrines with specific features, such as handrails and a seat, because some of these people will be incapable to squat (section 3.5 Further reading). Additional attention will have to go to the earth mound, like a more gentle slope. An access ramp will be essential for people in a wheelchair.


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Make sure that correct hand washing facilities with water and soap (or ash) are provided in the direct neighbourhood of the raised pit latrines. Make sure that the wastewater facilities are maintained correctly.


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Insecticide Residual Spraying (T.B. 7.15) of the raised pit latrines’ interior superstructure walls has potentially a high impact on the fly population.


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The operation and maintenance activities are similar to the type of latrine chosen, e.g. simple pit, VIP or twin pit latrines (T.B. 3.04; 3.07; 3.09).


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Due to the contamination risks, latrines should not be emptied manually, except if they have been closed down for at least two years. The design of the latrine should permit manual emptying (e.g. twin pit latrine). However, in many countries, this practice is socio-culturally not acceptable for the population.


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This system, which is often used for sludge trucks, is very effective because it “sucks” up the sludge by means of under-pressure that is created in a sewage tank. As the moving parts of the “vacuum” pump don’t get in contact with the sludge, the breakdown frequency of such a pump should normally be low. Another advantage is that this system can be used (at least theoretically) for all kinds of excreta disposal systems (latrines and septic tanks), as long as the sludge is still liquid enough (this is not the case for twin pit and Eco-San latrines that transform faeces into solid compost). The liquid sludge of septic tanks and latrines is emptied quite quickly. However, this fast “suction” can lead to the collapse of partially lined or unlined pit latrines. The other inconvenience is that these systems are very expensive.


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Although resembling motor pumps used for water, trash pumps have some specific features. Their inlet isn’t located at the centre of the impellor, but above. Their impellor has only a few solid blades, potentially with cutting edges. Another difference with a motor pump is that their pump house can easily and rapidly be opened for de-blocking and cleaning purposes. Hence, these centrifugal trash pumps are specially designed to drain liquid sludge that contains quite some solid particles (e.g. with diameters up to 30 mm). They can be used to empty septic tanks or latrine pits containing a lot of liquids. The use of a strainer with rather big holes is obligatory.


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These volumetric pumps are specially designed to drain sludge still containing relatively big solid particles (e.g. with diameters up to 60 mm). So they are suited to empty septic tanks and latrines if their sludge is liquid enough. The maximum delivery head and flow (T.B. 2.26) of a diaphragm pump are only half or even less of those of a trash pump with a similar engine, but it can deal with double sized particles. These membrane pumps are often driven by combustion engines. The use of a strainer with rather big holes is advised.


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These centrifugal pumps have to be lowered in the sludge. Depending on their hardness, potential “solid” particles present in the liquid sludge (up to a certain size) will be grinded into small pieces by the cutting blades of the impellor. These pumps aren’t really suited for latrines having their slab fixed on the pit because their diameter is often too big to be lowered via the defecation hole. These pumps are more appropriate to empty septic tanks. As an electrical motor drives this kind of pumps, an adapted generator will often be needed for field use. Verify if the chosen generator is adapted to the starting current of the pump motor.


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In the early stages of an emergency when no other alternatives are available yet, a standard 3” motor pump can be used to empty the emergency latrines, at least when they contain a lot of liquids. This can be the case for latrines built in an underground that doesn’t have a high infiltration rate (e.g. clayey soil; T.B. 4.05) and where the users do anal cleansing with water. The sludge can also be liquefied more by adding water before the pumping starts, but this increases the risk of the latrine pit collapsing. A motor pump used for emptying sludge should never be used anymore for other purposes, and certainly not for potable water!


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Sludge trucks / “vacuum suction” systems have their transport tank integrated. For the other pump systems, (round) metallic or solid plastic tanks can be used. They need to be leak proof and have big drains to ease the removal of the sludge. The tanks have to be correctly fixed to their transport means (e.g. a truck) to avoid accidents. In the very first phase of an emergency, a 2 or 5 m³ (transport) bladder can be used if no other means are available at all. This bladder should never be used anymore for other purposes afterwards, certainly not for potable water!


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Never empty a latrine / septic tank manually with recipients such as a bucket. Pathogens present in the sludge are serious health hazards to the workers. The only exceptions are the twin pit latrines where the excreta has been transformed into harmless compost (at least if the decomposition time of minimum 2 years has been respected) or where ecological sanitation systems are used (Eco-San is only briefly mentioned in these guidelines).


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Always verify if a municipal or private sludge truck is available (for rent) in the region. Before signing a contract with the owners, check if the sludge truck functions properly, how much capacity it has, where they dump the excreta and if they have the permission to do so.


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All systems, except the submersible grinder pumps are “suction” systems, thus they are not able to remove sludge out of deep pits (and certainly not deeper than 7 m) and/or pits that are located far from the “suction” system because the liquids can be quite viscous.


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All the equipment and the surroundings that have been in contact with the sludge should be thoroughly rinsed with clean water immediately after the works.


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Equipment that has been into contact with sludge should never be used anymore for other purposes afterwards.


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Make sure that the sludge tanks don’t leak because they will leave a contaminated trail over the whole transport route.


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The sludge should be buried at a safe place where it will not cause any public health or environmental risks, or it should be brought to a certified treatment plant (although that the latter is not often available in low-income countries). The burial trench should be at least 800 m away from dwellings, 50 m away from water points, and for homogeneous soils at least 1.5 m above the highest possible groundwater table (at the end of the rainy season). The required vertical distance for heterogeneous soils is difficult to predict however.


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Regular checks should be performed to verify if the sludge is correctly disposed of at the right spot.


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Make sure that the operators have good protective clothing and do wash thoroughly their hands with water and soap after finishing the job (e.g. before the lunch, at the end of the working day). Daily showers are also highly recommended. Do foresee the necessary facilities for these essential hygiene practices.


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The health risks due to pollution carried by wastewater as well as the presence of stagnant water are the following:


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Chemical contamination of water (e.g. nitrates, detergents) and ecological disturbance / pollution of aquatic environments (ground and surface water);


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Other nuisances are runoff water and wastewater entering in and/or causing erosion to shelters and other buildings, roads, pit latrines, waste pits which can lead to difficult and unsafe access to these facilities and even bigger health risks (e.g. flooded latrines which spread the excreta all over).


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A clear distinction has to be made in between runoff water (e.g. rainwater that doesn’t infiltrate naturally in the ground) and wastewater (used water). As long as the runoff water doesn’t get in contact with waste (water), it isn’t considered being contaminated, thus it doesn’t need real “treatment”. However, standing runoff water can be a breeding ground for vectors, and thus needs to be removed via a separated evacuation system.


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Risks associated with wastewaters depend on their origin and thus their degree of pollution, and it is useful to classify them as following:


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➞ Sewage (black water): water carrying excreta in suspension, thus containing bacteria, viruses, faecal parasites and also nitrogen.


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➞ Sullage (grey water): water from water distribution points, kitchens, (hand) washing areas and from health centres, often containing detergents (with nitrogen and phosphorus components), grease and fats, as well as (faecal) micro-organisms, suspended and/or dissolved organic matter.


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➞ Sullage coming from laboratories: they may contain hazardous chemical substances, as well as micro-organisms (e.g. of faecal origin).


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➞ Liquid residues from water treatment systems: backwash water or sedimentation sludge will be highly concentrated with dirt and chemicals when coagulants are used.


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All runoff water should always be controlled to avoid risks of flooding or stagnant water. In order not to contaminate the big amounts of runoff water that can’t be infiltrated, a separated and appropriate evacuation system for the wastewater and the rainwater has to be foreseen.


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For every situation where water is supplied, there will be wastewater generated. Therefore, there should always be a removal and “treatment” system, which prevents stagnant water and local contamination of potable water resources.


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User points: e.g. kitchen, laboratory, showers (T.B. 4.01), washing areas (dishes, bathing, laundry; T.B. 4.02), hand washing stations.


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Appropriate facilities should always be foreseen close to the site where the wastewater is generated. Wastewater from laboratories (mixed with chemicals) and health structures do often demand some extra attention however. In these cases, additional support must be required from your technical referent.


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The construction, operation and maintenance should be discussed and agreed upon with all the stakeholders (e.g. aid-agency, population, local authorities) in order to have the facilities build, used and maintained correctly (e.g. no washing at water points lacking a grease trap, no dumping of solid waste in the open drainage canals). Health promotion activities can help to achieve this.


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For correct planning and organisation of runoff water and wastewater disposal, it is necessary to follow all the different steps described in chapter 1. Within a humanitarian context, a lot of the facilities that generate and dispose of wastewater will have to be provided according to the essential water and sanitation requirements for health structures or camps (T.B. 1.08; 1.09), but adapted to the needs, habits and culture of the beneficiaries (e.g. traditionally, do the people stand or kneel during laundry activities). The more users’ friendly and appropriate the facilities are, the more they will be used. Information and promotion activities will need to be organized for the population to use and maintain the facilities correctly.


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A removal system should be able to evacuate runoff water or wastewater, so as to avoid stagnant water, and to channel it to the treatment / disposal site without contaminating the local environment. The collection surface for runoff water or wastewater should be gently sloped (at least 1%) and preferably cemented. The removal system design may be based on different techniques:


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This is the most simple and least costly technique but it entails maintenance problems: e.g. blockages, stagnant water, damage to the sides of the channel, people dumping their garbage in it. This technique should only be used for drainage of runoff water or for evacuation of sullage over short distances. The channel should preferably be cement-lined and with enough slope to be self-cleansing (about 1.5%). In case cement-lining would be impossible, the open channel could be reinforced with boulders to avoid collapse but leaving enough gaps for the water to pass easily.


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For sullage, a wide piece of plastic sheeting can be laid in an open channel, filled up with coarse gravel and finally folded over the gravel to form a sort of pipe. The whole gravel drain should be covered with an earth layer. As this type of drain is impossible to unblock, the sullage should never contain suspended or greasy material. It should only be used in (the early stages of) an emergency, for example at a dispensary or a laboratory.


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This is the most effective way of removing runoff water and all kinds of wastewater, but also the most expensive one. Various types of pipe may be used (e.g. PVC, polyethylene, cement), with a minimum diameter of 100 mm. The slope (minimum 1% and minimum 1.5% for black water) and the pipe diameter should be adequate for the flow, and the pipes should be buried. Special care should be taken at crossing places of vehicles and big animals (e.g. plastic pipe covered by concrete slabs or installed within a bigger diameter steel pipe). Manholes and collection boxes (T.B. 4.03) should be included when long and/or complex drainpipe systems are installed. These can help during the regularly needed checkups in order to deal with blockages.


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It may be necessary to pre-treat the water to remove solid or dissolved matter that could hamper the removal and/or the final disposal:


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Grease-trap (T.B. 4.04) to eliminate oily and greasy material (e.g. soap) in wastewater (sullage). The sand and grease trap can be combined.


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If not well operated and/or maintained, all these structures can block the wastewater system and possibly become ideal vector breeding sites as well.


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Where rainwater doesn’t infiltrate naturally in the ground within few hours, the runoff water can be evacuated directly to surface water like rivers or streams, but downhill of existing water intake points. Swamps or lakes can also be considered as possible evacuation locations when no water is taken for consumption at these places. As runoff water shouldn’t be contaminated, the evacuation can be done without specific treatment, except possibly the removal of floating and bulky objects.


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For wastewater however, many different techniques exist and the choice of a system, or a combination of several, depends on the type and the quantity of wastewater to be treated.


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In settings of low-income countries, the methods, as described in these guidelines, should be as simple, as affordable and as durable as possible, so that they can continue to be operational. Completely natural treatment methods are therefore preferable. Infiltration combines the final disposal with a form of natural treatment. It uses the natural capacity of the soil to fix particles present in the water by filtration, and to purify the water by a process of biological decomposition capable of retaining organic matter including micro-organisms, and some chemical pollution.


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A mature organic-rich soil is host to intense biological activity favouring purification, but it blocks rapidly and so has a reduced infiltration potential;


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Conversely, a sandy soil (generally considered as a good filter) with coarse structure may have an infiltration rate which is too rapid and which does not allow sufficient time for purification if the water table is too close to the surface;


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The slope of the ground (topography; T.B. 2.24): a slope too steep may encourage water to remerge and thus to contaminate the ground surface.


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The groundwater level: a high level (e.g. during the rainy season) will increase the risk of groundwater pollution and won’t permit the infiltration of large amounts of wastewater.


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The principle of infiltration / dispersal is used (sometimes in combination with other principles) in the following final disposal techniques:


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<table><tr><td/><td>Removal</td><td>Pre-treatment</td><td>Final Disposal</td></tr><tr><td>Runoff water</td><td>Channel, Drain</td><td>Not needed</td><td>River, Stream</td></tr><tr><td>Water point spillage</td><td>Channel, Drain, Pipe</td><td>Not needed</td><td>IT, SA, IF, ET, S</td></tr><tr><td>Sullage (grey water)</td><td>Pipe</td><td>Grease trap</td><td>IT, SA, ET, S</td></tr><tr><td>Sewage (black water)</td><td>Pipe</td><td>Septic tank</td><td>IT, SA, ET, S</td></tr></table>


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Removal Pre-treatment Final Disposal Runoff water Channel, Drain Not needed River, Stream Water point spillage Channel, Drain, Pipe Not needed IT, SA, IF, ET, S Sullage (grey water) Pipe Grease trap IT, SA, ET, S Sewage (black water) Pipe Septic tank IT, SA, ET, S


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If all final disposal methods for wastewater fail where it rains a lot, there is still the possibility to mix the pre-treated wastewater (floating and bulky objects, grease, fat, oil and excreta removed) with the runoff water and to drain everything away towards surface water. This dilution will reduce the concentration of pathogens and thus the risk of contamination. But the drainage should be done in an as large and as fast flowing river as possible, and downstream of sites where surface water is collected (e.g. water supply intake). It should also be verified downstream if other people than the beneficiaries do use the surface water for their daily needs and if the discharge has a potential negative impact on their health (e.g. by bacteriological analyses).


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Choose a site in the neighbourhood of dwellings / (health structure) buildings and close to a water point. The site should have enough space and capacity to infiltrate wastewater (T.B. 4.05).


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Prepare the site for construction: remove all debris, flatten the surface, install a temporary fence and bring in the needed construction material and equipment.


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Lay out the area with dimensions of at least 2.5 m x 2.2 m, using string lines. This size will permit to build a double shower, with a drainage channel included at the back.


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Excavate from this area all soil containing dust, hidden debris and decomposing vegetation (humus), and dig a little deeper at the back to prepare the open drainage channel.


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Make holes of another 0.4 m deep nearby the corners and in the middle of the area, with a snail house shape as indicated on the figure.


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Anchor plastic pipes in the holes, sticking vertically out of the ground by at least 0.3 m. These holes will facilitate the insertion of the superstructure poles in a later stage.


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Construct a casing for the slab and drainage channel, at least 0.1 m above the ground level. An alternative is to use only the excavation as casing and to build protective kerbs afterwards on the edges of the slab and drainage channel.


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➞ a stable but permeable ground, put a piece of plastic sheeting on the whole excavated area, including its edges and the casing.


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Prepare and cast lean concrete (150 kg/m³; T.B. 2.05) to form the slab and the drainage channel. The concrete should be vibrated to remove all oxygen. Once the concrete starts to settle, create for the slab a slope of 1 to maximum 4% towards the open drainage channel, needing itself a perpendicular slope of 1.5%. Try to obtain a smooth surface because it will help to drain the wastewater away. However, the slab should not become slippery as this could lead to accidents.


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Cover the slab and drainage channel with thick sacking that is regularly wetted or with plastic sheeting (that will keep the humidity inside), and let it cure for at least 1 week.


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Connect the shower via a grid and a grease trap (T.B. 4.04) to an infiltration system like a soak away pit (T.B. 4.06), an infiltration trench (T.B. 4.07), an evapo-transpiration area (T.B. 4.08) or a closed sewer system.


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Make a superstructure with poles and plastic sheeting or waterproof local material. It is strongly recommended to install a roof over the showers with separate drainage to avoid too much rainwater evacuating via the grease trap and infiltration system, which will eventually lead to their breakdown. If the separate drainage is extended around the structure, runoff water can be evacuated without eroding the showers.


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Make sure that the concrete slab and the superstructure of the showers are cleaned and disinfected with 0.1% chlorine solution (T.B. 2.20) every day.


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Make sure that the grid retaining solids from going into the grease trap and infiltration facilities is checked / cleaned on a daily basis.


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Drainage channel (1.5% slope)	 - String line, sticks and tape measure leading via a grate and grease trap to an	- Spirit level


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Several of these shower constructions can be put in rows. The amount of showers needed depends on the number of potential users (1 shower / 40 persons; T.B. 1.08; 1.09).


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The location of the shower unit should not be too remote from the dwellings / (health structure) buildings, to increase the comfort but even more to reduce potential sexual violence. The location should also permit to enter the shower in a discrete manner (e.g. not in the middle of a public court).


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An additional non-transparent screen in front of the entry side of the showers improves the privacy, which might lead to a more frequent use of the facilities. In certain cultures, the use of showers might drastically increase when they are integrated within a comfort zone together with latrines and washing facilities for sanitary towels. In other places, it might be better to keep the showers completely separated from the latrines, to avoid confusion in their use.


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It is also important in most cultures to have separated shower facilities for men and women. It is strongly recommended to have separated showers as well for the staff in health structures.


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In all cases, the showers should be adapted to the habits (e.g. bucket shower, overhead shower with running water) and the average height of its users. In case of overhead showers with running water, be aware that the water consumption will increase drastically, meaning that the capacity of the wastewater facilities will have to be adapted as well.


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Special attention should go as well to showers for physically impaired people. The water supply should be close to the showers and easy accessible. More space, a seat and handle bars should be available. It is recommended that in-patient health structures have such adapted shower facilities.


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The slab and drainage channel can also be made with bricks that are covered with cement plaster (T.B. 2.05), but this construction is generally less strong than concrete.


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It is recommended to install a hook within the superstructures to allow users to hang up their clothes.


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In places where people defecate in the showers, the bottom of the superstructure panels could start just above ankle height (about 0.2 m) to avoid people squatting down. This system cannot be used in all cultures, which has to be verified during the assessment.


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A good drainage with grid, settlement tank with grease trap and disposal / infiltration system is essential to avoid the shower area to become a puddle of stagnant water and thus a potential health hazard.


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Plastic bags are often used to transport the soap for washing. These bags are often discarded in the drainage system, which will clog up. To reduce this risk, a waste bin needs to be installed nearby the shower and its purpose explained to the users. Do not forget to empty and maintain the bin.


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In certain countries, the shower might be replaced by a sauna (beyond the scope of these guidelines).


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<table><tr><td>A washing area should provide a hygiene facility to do the laundry or the dishes, without creating</td></tr><tr><td>environmental health risks (e.g. stagnant water). Its design should be adapted to the habits of the</td></tr><tr><td>population, particularly concerning the position generally used by women to wash clothes or dishes</td></tr><tr><td>(e.g. crouching or standing up). The facility described here is about the simplest possible to build.</td></tr></table>


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A washing area should provide a hygiene facility to do the laundry or the dishes, without creating environmental health risks (e.g. stagnant water). Its design should be adapted to the habits of the population, particularly concerning the position generally used by women to wash clothes or dishes (e.g. crouching or standing up). The facility described here is about the simplest possible to build.


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Choose a site in the neighbourhood of the dwellings / (health structure) buildings and close to a water point. The site should have enough space and potential to infiltrate wastewater (T.B. 4.05).


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Lay out the area using a string line. An area of 1.5 m x 1 m must be considered as the minimum space needed for one user doing the laundry. A larger width will raise the comfort for the individual user, whereas the total length is linked with the potential number of persons using the facility at the same time. Be aware however that the bigger the size of a concrete slab, the higher the risk of cracking. So it is better to construct several washing facilities of reasonable size (e.g. 4 m length) instead of a huge one.


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➞ an unstable ground, spread a layer of sand and gravel on the whole excavated area and compact it well.


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➞ a stable but permeable ground, put a piece of plastic sheeting on the whole excavated area, including its edges.


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➞ a stable and impermeable ground, no specific features need to be foreseen; except if the excavated area is deep and requires some backfilling with a compacted layer of sand and gravel.


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Prepare and cast lean concrete (150 kg/m³; T.B. 2.05) to form the double sloped slab and the drainage channel. The concrete should be vibrated to remove all oxygen. Once the concrete starts to settle, create slopes of maximum 4% along the whole area’s length, both leading to the drainage channel in the middle, needing itself a perpendicular slope of 1.5% (the direction of all slopes are indicated by the arrows on the figure). Try to obtain a smooth surface because it will help to drain the wastewater away. However, the slab should not become slippery as this could lead to accidents.


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Cover the whole slab with thick sacking that is regularly wetted or with plastic sheeting (that will keep the humidity inside) and let it cure for at least 1 week.


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Construct on the circumference of the concrete slab a protective kerb with fired bricks or cement blocks, leaving an opening at the level of the drainage channel. The protective kerb should rise at least 0.1 m above the ground level.


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Cover all the surfaces of the protective kerb and collection box) with two layers of cement plaster (each 10 mm thick; T.B. 2.05), and smooth it well. Let it cure for several days, preferably a week.


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Connect the collection box of the washing facility via a grease trap (T.B. 4.04) to an infiltration system like a soak away pit (T.B. 4.06), an infiltration trench (T.B. 4.07), an evapo-transpiration area (T.B. 4.08), or a sewer system. To avoid the connection pipes in between the wastewater facilities getting blocked with big (waste) fragments, a grid should be installed inside the collection box.


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Install preferably a roof over the washing facility with a rainwater harvesting system (T.B. 2.09) and/or a separate drainage to avoid too much runoff water evacuating via the grease trap and infiltration facility, which will eventually lead to their breakdown. If the separate drainage is extended around the structure, runoff water can be evacuated without eroding the washing facilities.


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Make sure that the slab of the washing facilities is cleaned and disinfected with 0.1% chlorine solution (T.B. 2.20) every day.


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Make sure that the grid retaining solids from going into the grease trap and the infiltration facilities is checked / cleaned on a daily basis.


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The location of the washing facilities unit should not be too remote from the dwellings / (health structure) buildings to increase the comfort, but even more to reduce the potential sexual violence.


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If people prefer to wash clothes standing up, a raised concrete tub that can easily be emptied, or a raised slab (e.g. at table height) is required. Clothes or dishes are also sometimes washed within a basin or a 200 l drum cut in half.


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The number of washing facilities needed depends a lot on the habits of the users. It is also strongly recommended that every health structure has a washing facility.


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Special attention should go to the design of washing facilities used by pregnant women or/and (temporary) disabled people. Often, they won’t be able to crouch down, so (slightly) raised facilities (attention to the height) with the possibility to sit down, potential handle bars and sufficient space might in some cases be needed.


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Although similar facilities can be used for washing clothes or cleaning the dishes, it’s strongly recommended to separate both activities completely. Dirty clothes can contain faecal material, and are therefore incompatible with eating utensils.


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A good drainage with grid, grease trap and disposal / infiltration system is essential to avoid that the washing area becomes a puddle of stagnant water.


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In low-income countries, the cooking pots are quite often cleaned with sand / earth and water. To avoid the risk that the drainage / infiltration system blocks rather rapidly, a grease trap with integrated settlement tank is recommended. This can easily be obtained by making a standard grease trap bigger (standard size calculated according the maximum hourly flow of wastewater; T.B. 4.04). Mainly its depth will have to be increased to raise its storage capacity for the sand / earth.


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Plastic bags are often used to transport the soap for washing. These bags are often discarded in the drainage system, which will clog up. There is also the risk that food residues will be disposed of in the drainage. To reduce these risks, a waste bin needs to be installed nearby the washing area and its purpose explained to the users. Do not forget to empty and maintain the bin.


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Drying lines should be part of the washing areas in health structures. This helps avoiding people lying clothes on the ground to dry. A roof should be installed above the drying lines, certainly during the rainy season. It is also strongly recommended that where possible, the clothes and linen are ironed before being used again (e.g. for protection against Myasis).


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During the acute phase of an emergency in a camp, it is possible to make washing areas by using only plastic sheeting (the same as being used for temporary shelters). The ground surface within a shallow excavation must be carefully prepared and all sharp objects (e.g. stones, roots) removed. A sand – gravel mixture compacted within the excavation provides the slopes for the working surface and drainage channel. These slopes should be lined with a double thickness of plastic sheeting. The edges of the plastic should be fixed with stones and covered with well-compacted earth. This technique only lasts a few days because the plastic sheeting gets damaged very quickly and/or might get stolen.


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Foresee extra space for manholes / collection-distribution boxes at the described places, while digging the trenches for a piped wastewater evacuation and dispersal system. The size of the extra excavation depends on the depth of the piping system. The deeper the pipes, the deeper and also the wider the manhole / collection-distribution box (for people to enter completely) and thus their excavation need to be. This means also a serious increase in costs. The minimum operational inner size is 0.60 m x 0.60 m, to allow entering a device to unblock the system.


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Build the manholes / collection-distribution boxes out of concrete or masonry-work (fired bricks, cement blocks or stones according to what is available) and foresee holes for the pipes. The bottom of the manholes / collection-distribution boxes must be constructed with a gradient equal to the slope of the pipes they will be connected to (at least 1%), and have a shape that helps to lead the wastewater into the evacuation pipes.


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Install the pipes (diameter of at least 100 mm) in the manholes / collection-distribution boxes. Each evacuation (outlet) pipe should be at the same level as the bottom of their respective manhole / collection-distribution box.


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Make each manhole / collection-distribution box as watertight as possible by covering all its inner and outer surfaces with cement plaster (T.B. 2.05), and give particular attention to the pipes passages. For the outer surfaces, only one 10 mm layer is required, whereas internally it is recommended to add a second 10 mm layer once the first one has dried. Smooth the second inside layer well because this will ease the maintenance afterwards.


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Install a solid (watertight) lid on each manhole / collection - distribution box to avoid access to vectors.


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Backfill the space in between each manhole / collection - distribution box and its respective excavated hole with compacted soil.


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: - When pipe B isn’t located at the bottom of the box (as indicated on the figure), it’s an incoming pipe, and the facility functions like a collection box.


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When pipe B is located at the bottom of the box, it’s an outlet, and the facility functions like a distribution box (e.g. infiltration trenches; T.B. 4.07 and evapo-transpiration area; T.B.4.08).


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Two simple types of grease traps may be distinguished, and the choice between one of them will often be decided by the materials and skills available:


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With separating partitions until the bottom (better retrieval of solid material; “B type” on the figure).


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A middle zone where fatty material floats and accumulates at the surface, and where heavier solids settle to the bottom;


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An outlet zone where grease-free water flows out towards the underground dispersal system or the underground sewer system.


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Choose a place as close as possible to the site where the wastewater is generated, with easy access and in front of the dispersal system: soak away pit (T.B. 4.06), infiltration trench (T.B. 4.07), evapo-transpiration area (T.B. 4.08) or sewer.


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Design the grease trap and draw a detailed plan. It should be rectangular in shape with its in- and outlet as far as possible from each other. The effective volume of the grease trap (volume actually filled with wastewater) should be enough to allow a sufficient retention time of the wastewater for the oil and fat to be separated, and for the solids to settle. As a general rule, consider that the effective volume should at least be double the maximum hourly flow entering the trap; e.g. for 100 l of wastewater entering per hour during the peak moment, the effective volume of the grease trap should be at least 200 l.


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Prepare the site for construction: remove all debris, lay out the area, install a temporary fence and bring in the needed construction material and equipment.


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Excavate at the chosen place, along the evacuation pipe trench, the area for the grease trap. The excavation dimensions must be bigger than the size of the grease trap to be built.


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Build the grease trap using locally available means and materials like cast concrete or masonry-work (fired bricks, cement blocks or stones), and foresee openings for the pipes. Make sure that the casing sticks out of the ground by at least 0.1 m to avoid runoff water entering the grease trap.


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Position the inlet and outlet pipes (diameter of at least 100 mm) carefully in order to facilitate the flow and the operation of the trap (see drawings).


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Make the grease trap as watertight as possible, by covering all its inner and outer surfaces with cement plaster (T.B. 2.05), and give particular attention to the pipe passages. For the outer surfaces, only one 10 mm layer is required, whereas internally it is recommended to add a second 10 mm layer once the first one has dried. Smooth the second inside layer well because this will ease the maintenance afterwards.


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Install a removable cover, equipped with handles. It should fit well on the trap and have a certain weight to avoid unauthorized opening (by children for instance), but still light enough to be opened regularly by a single maintenance person (maximum 50 kg).


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Don’t forget to remove once in a while also the solids that have settled on the bottom of the grease trap. To ease this maintenance, a pump capable of pumping solids (e.g. motor pump, dewatering pump) and a recipient (e.g. bladder) can be used. This pump and the recipient can never be used anymore for potable water!


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Reference line indicating effective depth	- Cover (e.g. concrete, metal, solid plastic) (max. water level)	- Temporary fence material


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Even in situations where a (closed) sewer system exists, wastewater (grey and black) should be pre-treated before being released (at least respectively by a grease trap or a septic tank).


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Runoff water should never pass through the grease trap because it isn’t needed (contains normally no oil, grease or fat), and its effective volume would need to be huge to obtain a sufficient retention time for the high quantity of diluted wastewater.


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Concrete covers of grease traps are often a lot heavier than 50 kg, which explains partly why these facilities aren’t well maintained. If concrete is used for the cover, the grease trap should be designed in such a way that the lid is divided in several parts, but still closes tightly to avoid vectors entering. Other lighter and resistant materials like metallic sheets (treated against rust), aluminium or plastic should also be considered for the cover of the grease trap.


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The “B type” partition baffles help to reduce the amount of settled materials escaping from the grease trap. The (PVC) pipes passing through, or the honeycombed part in the partitions should be at least 100 mm above the bottom of the grease trap.


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Good maintenance is the key to an effective grease trap as it will limit odours and avoid fat and oil getting into the infiltration / sewer system.


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The oil and fat coming out of a grease trap should never be disposed of in an organic waste pit or a latrine. They would clog the vertical infiltration walls of the pit, therefore obstructing the liquids to infiltrate into the ground.


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To be able to perform the maintenance correctly, the staff needs protective clothing such as (watertight) heavy-duty rubber gloves, overall, mask, boots and other material such as collection and transport recipients, a pump, a wheelbarrow and shovels.


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The maintenance team should be able to recognize when a grease trap doesn’t function properly. Some indicators can be:


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In emergency situations and where the amount of wastewater is very limited (peak flow < 50 l/h), a grease trap can be constructed out of a 200 l drum, an elbow and a T-piece (according to the “A type”).


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Grease traps can also be made out of rectangular plastic containers, or even bought ready-made (importation probably needed).


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Soil texture is the relative proportion in percentage of sand, silt and clay-sized mineral particles in the fine-earth fraction of the soil. The physical properties of soils depend largely on their texture: e.g. sand is gritty and has very good drainage capacities, but it is unstable with regards to excavations; clay feels slick and sticky, and exhibits plasticity when mixed with water, to which it is relatively impermeable, but it is stable against collapse when dry; silt feels smooth and velvety (like flour). Loams are composed of sand, silt and clay, in different proportions, having an influence on their properties (e.g. water retention, plasticity, permeability).


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The soil texture can be determined on the field with the following test (adapted from Lindbo et al.):


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When pressing the ball between thumb and forefinger, does the soil form a ribbon that extends beyond the forefinger?


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Wet a small sample of the ribbon excessively in the hand palm and rub it with the forefinger. If it feels: gritty ➞ Sandy loam


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Wet a small sample of the ribbon excessively in the hand palm and rub it with the forefinger. If it feels: gritty ➞ Sandy clay loam smooth ➞ Silty clay loam neither ➞ Clay loam


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Wet a small sample of the ribbon excessively in the hand palm and rub it with the forefinger. If it feels: gritty ➞ Sandy clay


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Although the determination of the texture gives already an indication on the permeability of the soil (see table hereafter), it is recommended to do a percolation test as well.


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Make at least 3 test holes, each one with a diameter (D) of 0.15 m and 0.5 m deep on the proposed site.


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Fill the holes completely with potable water and leave overnight (or at least for several hours) to bring the soil to a saturated state.


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Fill the test holes the next day with potable water to a height of 0.3 m (if the water levels in the holes are still at or above 0.3 m height overnight, the permeability will certainly be too low for infiltration systems).


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Calculate the average difference in water levels of the three holes (h) corresponding to this period of 60 minutes, in order to determine the average water volume (Vav) that has been infiltrated per hole:


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Extrapolate this average infiltrated water volume per hole (vertical infiltration area of about 0.15 m²) to an infiltration surface of 1 m² over a 24 hours period in order to obtain the infiltration rate in l/m²-day:


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Compare the result with the infiltration rate values of potable water for different soil textures represented in the table hereafter. Thus an indication for the infiltration rate of wastewater for this soil is obtained as well.


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In case the water table level isn’t a limiting factor for the design of a soak away pit, its diameter can be chosen and thus the minimum depth calculated. It is recommended however for safety reasons that an unlined soak away pit doesn’t exceed a depth of 2 – 3 m (depending on the soil texture).


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The 0.5 m is the estimated depth of the pipe outlet and the surface above isn’t effective for infiltration. This supplementary depth might have to be adapted to the real depth of the pipe outlet.


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If the water table level is relatively high and represents thus a limiting factor for the soak away pit’s depth, the diameter will have to be adapted to the maximum depth that can be admitted. Make sure that the bottom of the soak away pit is always at least 1.5 m above the highest water table level (rainy season). Following formula can be used:


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Once the effective infiltration surface is known, the length of infiltration trenches can be calculated:


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The effective depth is the infiltration height underneath the perforated pipe The bottom of the trench should be at least 1.5 m above the highest water table.


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At least two trenches of 25 m length will be required (the maximum length of a single infiltration trench is limited to 30m). An alternative is to make infiltration trenches with the typical trident form (T.B. 4.07); each trench with a minimum length of 17 m. Notice that only the vertical surfaces (and not the bottom) of the trench have been taken into account in the calculation of the infiltration surface.


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Each time a pit or trench has to be dug, soil texture tests should be performed to determine the risk of collapse. The soil texture might change as the excavation gets deeper. Therefore might it be necessary to repeat the soil texture test at different depths, certainly when the colour of the soil changes and/or when it feels differently. It is also recommended to do soil texture tests at different places along a trench excavation. The soil humidity also plays a role in its stability (the wetter, the faster it will collapse).


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Pits with a partial lining (T.B. 3.04) can be excavated in soils with sand or loamy sand textures to a depth of 2 m only, whereas the depth can be increased to 3 m in soils with mainly dry loam and/or dry clay textures.


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The table represents the approximate infiltration rate estimations of potable water and wastewater according to the soil texture:


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Soil texture	Infiltration rate of	Infiltration rate of potable water (l/m²-day)	wastewater (l/m2-day)


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This method of evaluating the soil permeability depends very much on the homogeneity of the soil. Therefore, a single percolation test has to be taken with precaution, as its results might not always represent the reality. It is advised to perform several percolation tests over the foreseen length of long trenches. As the excavation progresses, a number of percolation tests should also be done at different depths, certainly when the colour of the soil changes and/or when it feels differently. However, as such a test is quite time consuming, it isn’t required for pits constructed during acute emergencies.


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As the percolation test is done with potable water, it does not take into account the clogging effect of the discharge of effluents carrying solids. Even spilled water at water points where there aren’t washing activities will contain some solids. But in general, the soil may be considered as having a sufficient infiltration rate for a dispersal system if the level in each hole of the percolation test falls at least by 0.10 m during the 60 minutes period.


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It has been found that in the long run, the infiltration rate for different soil textures is more or less the same once the soil surface is partially clogged. To be on the safe side, it’s better to work on the basis of 10 l/m²-day for the infiltration of wastewater effluents and 20 l/m²-day for water from a water point where no washing activities are done (e.g. tap stand).


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Be aware that the greater the permeability of the soil (good infiltration), the higher the risk of the wastewater contaminating the (ground)water. This should be taken into account for the vertical distance in between the bottom of pits / infiltration systems and the groundwater table. For homogeneous soils, the minimum vertical distance should be at least 1.5 m. It is also recommended as a general rule to install pits / infiltration systems downhill from groundwater points at a minimum distance of 30 m. This is to prevent microbiological contamination of the groundwater if wastewater would infiltrate until the aquifer. The minimum distances (vertically and horizontally) are difficult to predict for fissured soils, unfortunately.


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It is important to know that when the infiltration capacity of an underground dispersal system (e.g. soak away pit, infiltration trenches) is calculated, only its vertical surfaces (and not the bottom) can be taken into account. This is due to a bacteria layer that will form rather quickly on the bottom of the dispersal systems, which will become impermeable after a while, and thus inhibit all infiltration.


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In case you would notice that your first infiltration facility doesn’t function as predicted by the permeability test, do not hesitate to construct new ones with oversized dimensions or change the technique (e.g. evapo-transpiration; T.B. 4.08).


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Choose a site as close as possible to the grease trap, but at least 6 m from dwellings, 7.5 m from trees or hedges and 3 m from property boundaries. The site should preferably be downhill and at least 30 m away from (ground)water sources if it is a “domestic” soak away pit.


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Determine the dimensions of the soak away pit, based on soil texture and permeability tests (T.B. 4.05), the level of the water table and the quantity of wastewater to be infiltrated.


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Dig the trench for the incoming pipe, with a slope of at least 1%, 0.3 m wide and at least 0.3 m deep.


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Dig a circular pit to the required dimensions. Measure the effective depth from the bottom of the incoming trench until the bottom of the pit. If the pit is deep and/or the soil is unstable, support the sides with wooden planks and poles during the excavation.


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Fill the soak away pit with stones up to the level of the trench bottom. The stones should be clean, with a diameter of 0.05 to 0.15 m.


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Lay, potentially on a layer of sand, the incoming pipe (min. diameter 100 mm; at least 1% slope) until the middle of the pit. Clear the stones around the pipe end to create an empty space to aid flow dispersal.


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Place a large flat stone over the end (outlet) of the pipe and add a layer of stones (at least 0.1 m thick). If a flat stone can’t be found, a concrete plate can be used as well.


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Fill the hole with earth and compact it and plant grass on top if the water and/or wind erosion is severe.


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Soak away pits can only infiltrate limited amounts of (pre-treated) wastewater. To determine the dimensions of the pit, it is important to evaluate the infiltration capacity of the soil and to allow for a possible increase in the amount of wastewater to be disposed of. Be aware that the infiltration will only take place via the vertical walls of the pit, thus its bottom should not be included as infiltration surface (due to an “impermeable” bacteria layer forming on the bottom).


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The bottom of the soak away pit should be at least 1.5 m (preferably 3.0 m if connected to a septic tank) above the highest possible water table (during the rainy season). If the groundwater table is rather high, opt for infiltration trenches (T.B. 4.07). The depth of the water table can be estimated by verifying its level in nearby wells. Another option is to drive a metal bar such as a reinforcing rod or (several pieces of) ½” galvanized pipe in the ground, as deep as 1.5 m beneath the required pit depth. When pulled out, the rod or (the earth inside) the pipe should be dry. Soil saturated with water after heavy rainfall might give a false impression of the actual water table level.


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Even with a water table that is always very deep, it is recommended to restrict the depth of a soak away pit (preferably to 3 m maximum) to limit the risk of collapse during the excavation works.


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If stones aren’t available for the reinforcement of the soak away pit, tree branches or bamboo can be used to construct a circular lining. But soak away pits made with these materials have a shorter lifespan (maximum 2 years),and are therefore only admissible during (the acute stages of) an emergency. Soak away pits are sometimes also lined with masonry-work or even concrete rings, with a concrete slab on top. Make sure that these models have enough holes in their lining to drain the liquids through their sides. Anyhow, their infiltration surface will be drastically reduced due to the lining. As these kinds of soak away pits are already a serious investment, infiltration trenches are probably a better option for sullage. Lined soak away pits can be a rather cheap alternative however for pour-flush toilets in comparison to a septic tank.


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There is sometimes a tendency not to cover the soak away pit with compacted earth, certainly in dry and hot areas. The idea is to use the heat of the sun assisting in the evaporation of the wastewater. Nevertheless, it is strongly recommended to cover the soak away pit as the geo-textile or perforated plastic sheeting over the stones prevents soil from getting between the stones and clogging the system, but still permitting air to get in and gasses to come out of the pit.


