This involves purification of water more acceptable for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses including being safely returned to the environment. Water treatment removes contaminants or reduces their concentration so that the water becomes fit for its desired end-use. The type of treatment is specific to the source of water and the type of contaminants. The treatment processes include physical, chemical and biological treatment options.

Some of the common methods include sedimentation, aeration, pH neutralization, disinfection methods such as chlorination and UV treatment and membrane filtration systems.