Frequently asked questions

1. Are filters used in other countries ?

Yes, Bio-Sand Filters are being used in more than 40 countries, according to Although the technology is spreading rapidly, the countries are primarily in Central and South America, Caribbean, Africa and India.

3. Do filters need maintenance, chemicals, electricity ?

Bio-Sand Filters do not require chemicals, electricity, or any moving parts. There is virtually no maintenance. Continued use of the filter, especially very sediment-filled (“turbid”) water, can cause the gaps (“spore openings”) between the fine sand grains to fill with debris, in turn reducing flow rates. Householders can stir the sand and remove the sediment-filled water. Normal flow will return to the filter once the fine sand is cleared of sediment. After cleaning, a re-establishment of the bio-layer takes place, quickly returning the purification efficiency.

5. How long does it take to make a filter ?

About 15-22 days. Poured concrete sits in the mold for 1 day, and then the mold is removed. Containers are filled with water and stand for 14-21 days to let the concrete cure. Kolar filters are painted on the outside in distinctive colors. Once a filter is delivered to a household, installation takes about an hour.

7. How is a filter installed ?

SAPWII staff transport the concrete tank to the household and hand-carry the container into the house to place in position. Three layers of gravel, course sand and fine sand, then a splash plate are placed in tank one by one. Staffers are specially trained to install the filter media in an exact sequence. Two or three test batches of water are poured through the filter to remove residual dust. The filter is ready to use.

9. Are filters used outside of homes ?

Yes. Bio-Sand Filters are ideal for schools, dormitories, bus stations, clinics, restaurants, small hotels, offices, workshops, et cetera, where there is a high-volume need for clean water. Several filters supplied by a cistern can become water-bottle filling stations. One successful design for a drinking-water kiosk includes a ground-level supply tank to receive water. A hand-pump is used to fill a rooftop cistern connected to 3-4 Bio-Sand Filters below. Users press a release valve to let cistern water into a filter as needed, and instantly receive clean water in their water bottles or jugs.

11. Do filters have a pump ?

No. Gravity moves the water. The weight of the water poured into a filter pushes the clean water down through the media layers, then up the discharge pipe and out the spout.

13. What can reduce a Bio-Sand Filter’s effectiveness?

Although a properly constructed and installed filter is virtually foolproof, there are situations that can reduce it’s effectiveness including:

  • Diffuser plate can be out of position, which allows the force of the water to disrupt the bio-layer.
  • Resting water level is too great, thus reducing oxygen flow to bio-layer.
  • Bio-layer has not yet matured.
  • Inconveniently located in household thus reducing use.
  • Flow rates too fast due to incorrect sand or gravel media layers.
  • Exit spouts are allowed to become dirty.
  • Receptacle containers are not clean.

2. How many people can one filter supply?

Once filter can easily supply clear, clean household drinking water for up to 45 people. Typically the daily capacity of a filter is more than enough to service a household of 15 people. A home of 12-15 can use.

4. How much do filters weigh ?

A fully loaded filter with concrete tank and sand/gravel layers weighs about 260 pounds. The concrete tank alone weighs about 160 pounds, media about 50 pounds, and "resting" water about 50 pounds. Users benefit from the weight because filters are too heavy to easily move, which could disturb the bio-cap or sand layers and reduce the effectiveness of a filter. Filters were designed for household use initially. Experience shows that larger filter containers are not as readily accepted for households due to size, and are more difficult to deliver when conditions are steep or remote.

6. How long will a Bio-Sand Filter last?

25-30 years. The concrete container is heavier and more durable, than the shorter-life plastic or ceramic containers. If a filter is not knocked over and cracked, a filter can last for decades. Because no consumables, such as chemicals, electricity, fuel, moving or exterior parts, are used, the operating costs are negligible.

8. Is the water only for drinking?

Bio-Sand Filters produce clean water. Most households use the water for cooking and bathing as well as drinking. Households are encouraged to use clean filter water for all their household water needs. Care should be taken to store clean filter water in clean, covered containers to avoid recontamination of the clean water. Clean recycled plastic water bottles are encouraged.

10. Why doesn’t the filter become polluted or clog up over time ?

The biological pathogens are consumed by the bio-layer organisms. As for sediment, continued use of very turbid water can plug the fine sand grains at the top of filter. The sand and water layer can be stirred and the sediment-filled water removed to restore flow rates. Although the Bio-Sand Filter does remove more than 90% of bacteria, which is often below infectious levels, it is recommended for infants and elderly people that filtered water also be disinfected by boiling or disinfectant for maximum purification.

12. Can you connect multiple filters together ?

Yes. The best practice is to supply water to standalone filters from a common cistern, rather than piping filtered water to a shared receptacle. Bacteria and pathogens could accumulate in a connecting pipe between filter spouts, contaminating water before it reaches the clean-catch receptacle.

14. What happens to the clean water after it is filtered ?

Water pours into a clean vessel, often a plastic or copper jug or water bottle. The receptacle is ideally covered and stored in another area, typically the kitchen or bathing area, until clean water is needed. There is an ongoing need for proper education regarding clean water, including storage, clean glasses and pots or capped water bottles. SAPWII has developed special education programs for school children about clean water use.