Following steps are involved in the purification of water:
(i) Firstly all the physical impurities like stones, plastic bags, cans etc. are to be removed. It is done by passing the water through bar screens.
(ii) Then water is taken to grit and sand removal tank where impurities are removed by sedimentation.
(iii) Solid impurities and feaces etc. are collected from bottom of water. These impurities collected are called sludge.
(iv) Clarified water is cleaned of other impurities by aerator. All disease causing bacteria are removed by chlorination.