Water fluoridation is the controlled adjustment of fluoride to a public water supply solely to reduce tooth decay. Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride.[2] 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.[3] Typically a fluoridated compound is added to drinking water, a process that in the U.S. costs an average of about $1.32 per person-year.[2][4] Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits.[5] In 2011, the World Health Organization suggested a level of fluoride from 0.5 to 1.5 mg/L (milligrams per litre), depending on climate, local environment, and other sources of fluoride.[6] Bottled water typically has unknown fluoride levels.[7]
Tooth decay remains a major public health concern in most industrialized countries, affecting 60–90% of schoolchildren and the vast majority of adults.[8] Water fluoridation reduces cavities in children, while efficacy in adults is less clear.[9][10] A Cochrane review estimates a reduction in cavities when water fluoridation was used by children who had no access to other sources of fluoride to be 35% in baby teeth and 26% in permanent teeth.[9] Most European countries have experienced substantial declines in tooth decay, though milk and salt fluoridation is widespread in lieu of water fluoridation.[11] Some studies suggest that water fluoridation, particularly in industrialized nations, may be unnecessary because topical fluorides (such as in toothpaste) are widely used, and caries rates have become low.[3]
Although fluoridation can cause dental fluorosis, which can alter the appearance of developing teeth or enamel fluorosis,[3] the differences are mild and usually not an aesthetic or public health concern.[12] There is no clear evidence of other side effects from water fluoridation.[13] Fluoride's effects depend on the total daily intake of fluoride from all sources. Drinking water is typically the largest source;[14] other methods of fluoride therapy include fluoridation of toothpaste, salt, and milk.[15] The views on the most efficient method for community prevention of tooth decay are mixed. The Australian government states that water fluoridation is the most effective way to achieve fluoride exposure that is community-wide.[12] The World Health Organization reports that water fluoridation, when feasible and culturally acceptable, has substantial advantages, especially for subgroups at high risk,[8] while the European Commission finds that while water fluoridation likely reduces caries, there is no evidence that it is more effective than topical application.[16]