Bio-Sand Filters are very simple in design. A large container is filled with coarse sand and water. After 20-30 days, a friendly micro-organic layer develops on the top portion of the sand. Dirty water is poured into the top of the filter. The water flows through the bio layer and then through the deep layer of sand.
By the time it comes out of the filter, approximate 99% of germs are eliminated, making it safe to drink.