One design brings the water in the top of a container through a “header” which distributes the water evenly. The filter “media” start with fine sand on the top and then graduating coarser sand in a number of layers followed by gravel on the bottom, in gradually larger sizes. The top sand physically removes particles from the water. The job of the subsequent layers is to support the finer layer above and provide efficient drainage.
Media filters are also used for c leaning the effluent from septic tanks and primary settlement tanks. The materials commonly used are sand, peat and natural stone fiber.