The MGF works on principle of retention and removal of physical impurity in a graded manner through Voids of the filtering media. Filter that makes use of fine media and coarse in a fixed proportion is termed as Multi grade Filter. It performs at a substantially higher specific flow rate than conventional filters.

Raw water passed through the Multi Grade Filter, it consists of multi layers of filter media consisting graded sand, white sand, fine sand, activated carbon and pebbles layers, which retain the suspended particles and activated carbon adsorbs onto its surface free chlorine, organic compounds, colour and odour. During the filtration cycle the filter bed retains the dirt and suspended particles from the water and accumulates within the filter bed. As the filtration progress the filter media gets loaded with the retained particles, this results in a continuous increase of pressure drop across the filter, when a predetermined pressure drop level is achieved the filter is shut down for cleaning.