What is a Bio-sand Filter?

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Travelling through Cambodia, visitors are struck by the number of children they see all around them. About one third of the population is under the age of 15. Unfortunately, more than 10% of these children don't live to be five years old. Dirty, disease-ridden drinking water causes about 20% of the deaths in these young children and contributes to serious malnutrition in most of the others.

A bio-sand filter is an inexpensive yet effective filter used to purify a water supply and prevent debilitating water-borne disease. It is a household adaptation of a slow sand filter developed by Dr. David Manz at the University of Calgary, Alberta. Studies have shown this filter removes more than 90 percent of harmful bacteria, 100 percent of parasites, 95 to 99 percent

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of iron, zinc, copper, cadmium, and lead, and suspended sediments. This filter does not effectively remove dissolved compounds such as salt and fluoride or organic chemicals such as pesticides and fertilizers. Filtered water is clear, odorless, and tasteless.

Each filter unit is constructed of a concrete body filled with layers of gravel and sand (see schematic). Source water is poured onto a diffuser plate at the top of the filter to prevent disturbing th top lay of sand. After passing through the sand and gravel, the purified water is delivered by displacement. Using the force of gravity alone it then travels up a copper tube and out the spout into a clean container ready for consumption. The key to the effectiveness of the filter is the biological layer that forms in the top four or five centimeters of sand over the first three weeks of filter use.

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This layer removes fine particulate matter and consumes bacteria and other pathogens. Proper storage of filtered water in clean covered container assures that the water remains pure.

The filter rarely requires cleaning that is easily done by agitating the sand surface and scooping out the suspended material. Other advantages include low cost, no power usage or moving parts, and manufacturing using locally available materials and labor. Each filter can produce enough drinking water to supply an extended family for many years at no cost.

Since early 2006 Water for Cambodia has built and installed thousands of bio-sand filters in over 150 villages throughout Siem Reap Province. They are providing clean, disease-free water to tens of thousands of rural villagers every day. The filters are built by local workers using materials that are locally available and they are installed with the help of project team members in homes, health centers and schools.