A Multimedia Filter is a gravity-type filter typically containing three media layers of anthracite coal, sand and garnet, with a supporting layer of gravel at the bottom. The entire media bed acts as a filter with efficient particulate removal as the upper layers removing large particles and the lower layers retain the smaller particles. This means it can be used for a long time before requiring backwashing. Multi Media Filter can remove particulates down to 15-20 microns. Also, if coagulants are used, they can remove particulates down to 5-10 microns by forcing the particles to merge into a larger one that can be easily filtered.