The practice of adding fluorine to water, usually drinking water.

Water fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay, and is handled differently by countries across the world.

The water fluoridation controversy arises from political, ethical, economic, and health considerations regarding the fluoridation of public water supplies.

Water fluoridation in the United States is common amongst most states.

alt=Water fluoridation in Australia (1964-1977 and 2012)|thumb|Amount of fluoride added to public water in ppm by postcode in Australia, 1964-1977 and 2012.