Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. In General, the following objectionable substances may be present in the raw water.

• Particulates in suspended or colloidal form.
• Inorganic compounds which precipitate or give rise to accumulations when their concentration is increased or the water is heated or the pH is changed.
• Organic compounds which will decay/decompose/degrade the drinking and service water systems due to their toxic properties.
• Bacterial impurities which are the cause of heavy growths of microorganisms and, thus, the formation of coatings and slime in pipelines, reservoirs, and heat exchangers.

In view of the above, the Raw water must be treated or clarified prior to being used as makeup water in most utility processes. Clarification removes suspended and dissolved solids, bacteria, and other forms of impurities to help prevent system scale, corrosion, and fouling.

Water treatment is any process that improves the quality of water to make it more acceptable for a specific end-use. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use.

The processes involved in removing the contaminants include physical processes such as settling and filtration and chemical processes such as disinfection and coagulation, and biological processes.

A combination selected from the following processes is used for municipal drinking water treatment raw water treatment for industrial purpose globally.