portable water purification portable water purification portable water purification devices are self-contained, easily transported units used to purify water from untreated sources (such as rivers, lakes, and wells) for drinking purposes. their main function is to eliminate pathogens, and often also of suspended solids and some unpalatable or toxic compounds. not to be confused with potable water. portable water purification unit used by international red cross and red crescent. these units provide an autonomous supply of drinking water to people without access to clean water supply services, including inhabitants of developing countries and disaster areas, military personnel, campers, hikers, and workers in wilderness, and survivalists. they are also called point-of-use (pou) water treatment systems and field water disinfection techniques. techniques include heat (including boiling), filtration, activated charcoal adsorption, chemical disinfection (e.g. chlorination, iodine, ozonation, etc.), ultraviolet purification (including sodis), distillation (including solar distillation), and flocculation. often these are used in combination. drinking water hazards untreated water may contain potentially pathogenic agents, including protozoa, bacteria, viruses, and some larvae of higher-order parasites such as liver flukes and roundworms. chemical pollutants such as pesticides, heavy metals and synthetic organics may be present. other components may affect taste, odour and general aesthetic qualities, including turbidity from soil or clay, colour from humic acid or microscopic algae, odours from certain type of bacteria, particularly actinomycetes which produce geosmin, and saltiness from brackish or sea water. common metallic contaminants such as copper and lead can be treated by increasing the ph using soda ash or lime, which precipitates such metals. careful decanting of the clear water after settlement or the use of filtration provides acceptably low levels of metals. water contaminated by aluminium or zinc cannot be treated in this way using a strong alkali as higher phs re-dissolve the metal salts. salt is difficult to remove except by reverse osmosis or distillation. most portable treatment processes focus on mitigating human pathogens for safety and removing particulates matter, tastes and odours. significant pathogens commonly present in the developed world include giardia, cryptosporidium, shigella, hepatitis a virus, escherichia coli, and enterovirus. in less developed countries there may be risks from cholera and dysentery organisms and a range of tropical enteroparasites. giardia lamblia and cryptosporidium spp., both of which cause diarrhea (see giardiasis and cryptosporidiosis) are common pathogens. in backcountry areas of the united states and canada they are sometimes present in sufficient quantity that water treatment is justified for backpackers, although this has created some controversy. (see wilderness acquired diarrhea.) in hawaii and other tropical areas, leptospira spp. are another possible problem. less commonly seen in developed countries are organisms such as vibrio cholerae which causes cholera and various strains of salmonella which cause typhoid and para-typhoid diseases. pathogenic viruses may also be found in water. the larvae of flukes are particularly dangerous in area frequented by sheep, deer, or cattle. if such microscopic larvae are ingested, they can form potentially life-threatening cysts in the brain or liver. this risk extends to plants grown in or near water including the commonly eaten watercress. in general, more human activity up stream (i.e. the larger the stream/river) the greater the potential for contamination from sewage effluent, surface runoff, or industrial pollutants. groundwater pollution may occur from human activity (e.g. on-site sanitation systems or mining) or might be naturally occurring (e.g. from arsenic in some regions of india and bangladesh). water collected as far upstream as possible above all known or anticipated risks of pollution poses the lowest risk of contamination and is best suited to portable treatment methods. techniques 31st marine expeditionary unit (meu) service support group 31 in leyte, philippines (feb. 20, 2006) not all techniques by themselves will mitigate all hazards. although flocculation followed by filtration has been suggested as best practice this is rarely practicable without the ability to carefully control ph and settling conditions. ill-advised use of alum as a flocculant can lead to unacceptable levels of aluminium in the water so treated. if water is to be stored, halogens offer extended protection. heat (boiling) heat kills disease-causing micro-organisms, with higher temperatures and/or duration required for some pathogens. sterilization of water (killing all living contaminants) is not necessary to make water safe to drink; one only needs to render enteric (intestinal) pathogens harmless. boiling does not remove most pollutants and does not leave any residual protection. the who states bringing water to rolling boil then naturally cooling is sufficient to inactivate pathogenic bacteria, viruses and protozoa. the cdc recommends a rolling boil for 1 minute. at high elevations, though, the boiling point of water drops. at altitudes greater than 6,562 feet (2,000 meters) boiling should continue for 3 minutes. all bacterial pathogens are quickly killed above 60 °c (140 °f), therefore, although boiling is not necessary to make the water safe to drink, the time taken to heat the water to boiling is usually sufficient to reduce bacterial concentrations to safe levels. encysted protozoan pathogens may require higher temperatures to remove any risk. boiling is not always necessary nor sometimes enough. pasteurization where enough pathogens are killed typically occurs at 63 °c for 30 minutes or 72 °c for 15 seconds. certain pathogens must be heated above boiling (e.g. botulism – clostridium botulinum requires 118 °c (244 °f), most endospores require 120 °c (248 °f), and prions even higher). higher temperatures may be achieved with a pressure cooker. heat combined with ultraviolet light (uv), such as sodis method, reduces the necessary temperature and duration. filtration portable pump filters are commercially available with ceramic filters that filter 5,000 to 50,000 litres per cartridge, removing pathogens down to the 0.2–0.3 micrometer (µm) range. some also utilize activated charcoal filtering. most filters of this kind remove most bacteria and protozoa, such as cryptosporidium and giardia lamblia, but not viruses except for the very largest of 0.3 µm and larger diameters, so disinfection by chemicals or ultraviolet light is still required after filtration. it is worth noting that not all bacteria are removed by 0.2 µm pump filters; for example, strands of thread-like leptospira spp. (which can cause leptospirosis) are thin enough to pass through a 0.2 µm filter. effective chemical additives to address shortcomings in pump filters include chlorine, chlorine dioxide, iodine, and sodium hypochlorite (bleach). there have been polymer and ceramic filters on the market that incorporated iodine post-treatment in their filter elements to kill viruses and the smaller bacteria that cannot be filtered out, but most have disappeared due to the unpleasant taste imparted to the water, as well as possible adverse health effects when iodine is ingested over protracted periods. while the filtration elements may do an excellent job of removing most bacteria and fungi contaminants from drinking water when new, the elements themselves can become colonization sites. in recent years some filters have been enhanced by bonding silver metal nanoparticles to the ceramic element and/or to the activated charcoal to suppress growth of pathogens. small, hand-pumped reverse osmosis filters were originally developed for the military in the late 1980s for use as survival equipment, for example, to be included with inflatable rafts on aircraft. civilian versions are available. instead of using the static pressure of a water supply line to force the water through the filter, pressure is provided by a hand-operated pump. these devices can generate drinkable water from seawater. the portable aqua unit for lifesaving (short paul) is a portable ultrafiltration-based membrane water filter for humanitarian aid. it allows the decentralized supply of clean water in emergency and disaster situations for about 400 persons per unit per day. the filter is designed to function with neither chemicals nor energy nor trained personnel. activated charcoal adsorption granular activated carbon filtering utilizes a form of activated carbon with a high surface area, and adsorbs many compounds, including many toxic compounds. water passing through activated carbon is commonly used in concert with hand pumped filters to address organic contamination, taste, or objectionable odors. activated carbon filters aren't usually used as the primary purification techniques of portable water purification devices, but rather as secondary means to complement another purification technique. it is most commonly implemented for pre- or post-filtering, in a separate step than ceramic filtering, in either case being implemented prior to the addition of chemical disinfectants used to control bacteria or viruses that filters cannot remove. activated charcoal can remove chlorine from treated water, removing any residual protection remaining in the water protecting against pathogens, and should not, in general, be used without careful thought after chemical disinfection treatments in portable water purification processing. ceramic/carbon core filters with a 0.5 µm or smaller pore size are excellent for removing bacteria and cysts while also removing chemicals. chemical disinfection with halogens chemical disinfection with halogens, chiefly chlorine and iodine, results from oxidation of essential cellular structures and enzymes. the primary factors that determine the rate and proportion of microorganisms killed are the residual or available halogen concentration and the exposure time. secondary factors are pathogen species, water temperature, ph, and organic contaminants. in field-water disinfection, use of concentrations of 1–16 mg/l for 10–60 min is generally effective. of note, cryptosporidium oocysts, likely cyclospora species, ascaris eggs are extremely resistant to halogens and field inactivation may not be practical with bleach and iodine. iodine iodine used for water purification is commonly added to water as a solution, in crystallized form, or in tablets containing tetraglycine hydroperiodide that release 8 mg of iodine per tablet. the iodine kills many, but not all, of the most common pathogens present in natural fresh water sources. carrying iodine for water purification is an imperfect but lightweight solution for those in need of field purification of drinking water. kits are available in camping stores that include an iodine pill and a second pill (vitamin c or ascorbic acid) that will remove the iodine taste from the water after it has been disinfected. the addition of vitamin c, in the form of a pill or in flavored drink powders, precipitates much of the iodine out of the solution, so it should not be added until the iodine has had sufficient time to work. this time is 30 minutes in relatively clear, warm water, but is considerably longer if the water is turbid or cold. water treated with tablets containing tetraglycine hydroperiodide also reduces the uptake of radioactive iodine in human subjects to only 2% of the value it would otherwise be, although the amount of iodine in a single tablet is not sufficient to block uptake. if the iodine has precipitated out of the solution, then the drinking water has less available iodine in the solution. tetraglycine hydroperiodide maintains its effectiveness indefinitely before the container is opened; although some manufacturers suggest not using the tablets more than three months after the container has initially been opened, the shelf life is in fact very long provided that the container is resealed immediately after each time it is opened. iodine should be allowed at least 30 minutes to kill giardia . iodine crystals a potentially lower cost alternative to using iodine-based water purification tablets is the use of iodine crystals, although there are serious risks of acute iodine toxicity if preparation and dilution are not measured with some accuracy. this method may not be adequate in killing giardia cysts in cold water. an advantage of using iodine crystals is that only a small amount of iodine is dissolved from the iodine crystals at each use, giving this method of treating water a capability for treating very large volumes of water. unlike tetraglycine hydroperiodide tablets, iodine crystals have an unlimited shelf life as long as they are not exposed to air for long periods of time or are kept under water. iodine crystals will sublimate if exposed to air for long periods of time. the large quantity of water that can be purified with iodine crystals at low cost makes this technique especially cost effective for point of use or emergency water purification methods intended for use longer than the shelf life of tetraglycine hydroperiodide. halazone tablets chlorine-based halazone tablets were formerly popularly used for portable water purification. chlorine in water is more than three times more effective as a disinfectant against escherichia coli than iodine. halazone tablets were thus commonly used during world war ii by u.s. soldiers for portable water