The main advantage of household water treatment is that it can be adopted immediately in the homes of poor families to improve their drinking water quality. It is also less expensive, more appropriate for treating smaller volumes of water, and provides an entry point for hygiene and sanitation education. There are a wide range of simple household treatment technologies that provide options based on what is most suitable and affordable for the household.
The biosand filter is a modified form of the traditional slow sand filter in such a way that the filters can be built on a smaller scale and can be operated intermittently. These modifications make the biosand filter suitable for household or small group use. The biosand filter can be produced locally anywhere in the world using materials that are readily available.
A bucket of contaminated water is poured into the top of the biosand filter. The water simply flows through the filter and is collected in another storage container at the base of the spout. A biological layer (often called the biolayer) of slime, sediment and microorganism develops at the sand surface. Pathogens and suspended material are removed through various physical and biological processes that occur in the biolayer and sand.
When water is flowing through the filter, oxygen is supplied to the biolayer by the dissolved oxygen in the water. During pause times, when the water is not flowing, the oxygen is obtained by diffusion from the air. If the standing water layer is kept shallow, enough oxygen is able to pass through to the microorganisms to keep them alive and effective.