To achieve better results in terms of specific flow and outlet quality multigrade filters are being used. Multigrade filter have more than one media for filteration. Other than filtering sand more poros media are utilized for filteration, entrasite and garnet are the examples of those kind of medias.
Because of their better porosity they are used as the primary filtering media along with the filtering sand as second level. The outlet of multigrade fiter can give less than 2 ppm turbidity.