The sedimentation process is used for the purification of water. The insoluble solid particles settle down at the bottom by the action of gravity when allowed to stand undisturbed. The speed of sedimentation of suspended particles can be increased by adding a chemical to the impure liquid. This is called loading. The chemical used for loading is potash alum.

Aeration is a step involved in the waste water treatment plants to disinfect water. Aeration is done after the filtration process. The filtered water, though it looks perfectly clear, it still contains germs. In the aeration process, air under pressure is blown into the filtered water to kill the harmful micro-organisms present in the filtered water. Thus, aeration helps in disinfection of water.