How Water is Filtered
The concrete Biosand filter is an innovative version of the slow sand filter specifically designed for household use. These filters are built locally using available materials and labor. As with the other types of water projects we support, we are meeting the clean drinking water needs of the region and providing needed jobs. Each community is a full participant in the project.
The Biosand filter is comprised of a container - plastic or concrete - and is about the size of an office water cooler. It has an inset plastic pipe and is filled with layers of sand and gravel. Dirty water is poured into the top of the biosand filter, where a diffuser plate evenly distributes the water over the sand bed layer. The water travels down through the sand bed, passes through multiple layers of gravel, and collects in the plastic pipe at the bottom of the filter. The clean water then exits through the plastic piping for a family to collect in clean containers.
The removal of contaminants and disease causing agents is possible due to a combination of biological degradation and mechanical filtration processes. The organic material present in the dirty water is trapped at the surface of the sand bed, forming a biological layer, or �schmutzdecke�, which actively removes pathogens and contaminants. The drinking water produced with the Biosand process is tasteless, clear in color, odorless and safe for drinking.
Studies have shown the Biosand filter can remove more than 90% of bacteria and 100% of parasites, dramatically increasing the safety of the water.
