A bio-sand filter is an age-old technology that is used to purify water. It’s constructed from building materials that are available everywhere in the world. The only materials required are sand, gravel, wood, and a binder for the cement case. Locals in East Africa are trained to source the materials, build the bio-sand filters, and test the final product to make sure that it removes contaminants from the water. Local teams can build these filters independently, without the need to rely on anyone outside of their community.
All water has good bacteria and bad bacteria. The good bacteria thrive at the top where there’s oxygen (aerobic bacteria). This good bacteria form a bio-layer at the top. When you pour water through the filter, the bacteria in the bio-layer kill the harmful bacteria in the water and purify it as it moves through the filter.