The bios and filter (BSF) is a simple household water treatment device. which is an innovation on traditional slow sand filters specifically designed for intermittent use. A BSF consists of a concrete or plastic container filled with specially selected and prepared sand and gravel. As water flows through the filter, physical straining removes pathogens. iron. turbidity and manganese from drinking water. A shallow layer of water sits atop the sand and a biofilm develops. The biofilm contributes to the removal of pathogens due to predation and competition for food of non-harmful microorganisms contained in the biofilm and the harmful organisms in the water