Water purification is the process of removing contaminants and other harmful microorganisms from a raw water source. 

Methods include, but are not limited to: ultraviolet light, filtration, water softening, reverse osmosis, ultrafiltration, deionization and powdered activated carbon treatment. According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply.

Governments usually dictate the standards for drinking water quality. These standards will require minimum / maximum set points of contaminants and the inclusion of control elements that produce drinking water. Quality standards in many countries require specific amounts of disinfectant (such as chlorine) in the water after it leaves the water treatment plant (WTP), to reduce the risk of re-contamination while the water is in the distribution system.  In the United States, the bottled water industry is not regulated to the standards that municipal water is.