Water fluoridation is the controlled addition of
fluoride to a
public water supply to reduce
tooth decay. Fluoridated water has fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride. Fluoridated water operates on tooth surfaces: in the mouth it creates low levels of fluoride in
saliva, which reduces the rate at which
tooth enamel demineralizes and increases the rate at which it
remineralizes in the early stages of cavities. Typically a fluoridated compound is added to drinking water, a process that in the U.S. costs an average of about $ per person-year. Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. A 1994
World Health Organization expert committee suggested a level of fluoride from 0.5 to 1.0 mg/L (milligrams per litre), depending on climate.
Bottled water typically has unknown fluoride levels.