ECHO regularly publishes agriculture technical notes to address important agriculture development issues. Here is a short excerpt from a tech note on Biosand Water Filter. It is available on ECHOcommunity.org
Access to clean drinking water remains one of the greatest challenges in the world. The BioSand Filter is one method that can be used for purifying water at the household level. With this filter, contaminated water is filtered through a natural biological layer and then layers of sand, pebbles and stones. The BioSand Filter can be made using local materials and is a low-cost system that removes suspended sediments and other impurities from water in order to make it safer for human consumption.
HOUSEHOLD WATER TREATMENT
Inadequate water and sanitation services result in an estimated 4 billion cases of diarrhea and 2.2 million deaths each year (WHO/UNICEF 2000). In areas where there is no access to potable water, household water treatment can contribute significantly to reducing water related health problems. The most effective water treatment methods follow a process of sedimentation, filtration, and disinfection to remove bacteria, viruses, helminthes, and protozoa.
The first known sand filter was made in Scotland in 1804 and since then slow sand filtration has been a common filtration method in the water treatment process. The BioSand Filter has adapted this technology to work at the household level, providing clean water at a maximum flow rate of 0.63qt (0.6lt) per minute. In the BioSand Filter, contaminated water is poured in at the top and is cleaned as it passes through a biological layer, a fine sand layer, a pebble layer, and a small stone layer
MATERIALS NEEDED FOR CONSTRUCTION
The complete article provides a detailed list of all material needed, including weight and measurement dimensions to construct an appropriate filter for home use.
Easy to follow instructions and diagrams on how to build the Filter Body and Diffuser Lid and Supply Container, makes this an attractive and easy project for a household in need of healthy drinking water to undertake.
This step-by-step description on how to assemble to filter reads like an easy to follow recipe and is accompanied by an illustrative diagram allowing for a visual of what the product should look like when assembled.
It takes approximately 3 weeks before he water is sufficiently filtered to be consumed without further disinfection. For best results use water from the same source to maintain the biological layer; keep the filter protected from dust and sunlight; keep the outlet clean; use a clean container for catching the filtered water. If the water to be filtered has lots of sediment or is very cloudy it should be allowed to settle before pouring it into the filter.
Over time the top of the fine sand layer will become clogged with sediment and debris and the flow rate will decrease. Cleaning frequency will depend on the amount and quality of water used.