Water purification is the process of removing contaminants from surface water or groundwater to make it fit for specific purposes. The contaminants may be particulate matter, dissolved minerals or microorganisms. Technologies commonly employed to purify water are distillation, ion exchange, adsorption, filtration, membrane filtration, ultraviolet (UV) radiation or a combination of more than one of these. The technologies most applied currently are membrane filtration and UV radiation. Nanotechnology is significantly advancing water purification technologies, especially in membrane processes.

The following technical classification has been arrived at, based on its commercial usage and popularity.

Note: Please note that the classification is only an indicative of the water purification market. It is not an exhaustive classification of water purification techniques.