Sedimentation: The process of allowing water to stand undisturbed in big tanks for some time in order to facilitate the settling down of the course suspended particles due to the force of gravity is called sedimentation. This is the process of removing suspended impurities by allowing the water to stand undisturbed in big tanks for 2 8 hours. Most of the suspended particles settle down at the bottom of the tank due to the force of gravity. The clear supernatant water is then drawn out. From the tank with the help of pumps. This process removes only 70 75%of the suspended matter.