𝐅𝐥𝐮𝐨𝐫𝐢𝐝𝐚𝐭𝐢𝐨𝐧 𝐨𝐟 𝐰𝐚𝐭𝐞𝐫

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, and some domestic water filters remove some or all fluoride. Dental caries remain a major public health concern in most industrialized countries, affecting 60–90% of schoolchildren and the vast majority of adults. Water fluoridation prevents cavities in both children and adults, with studies estimating an 18–40% reduction in cavities when water fluoridation is used by children who already have access to toothpaste and other sources of fluoride. Studies suggest that the use of water fluoridation particular in industrialized countries may be unnecessary for caries prevention, because topical fluorides (such as in toothpaste) are widely used and caries has become low. Although fluoridation can cause dental fluorosis, which can alter the appearance of developing teeth or enamel fluorosis, most of this is mild and usually not considered to be of aesthetic or public-health concern. There is no clear evidence of other adverse effects from water fluoridation. Studies on adverse effects have been mostly of low quality. Fluoride's effects depend on the total daily intake of fluoride from all sources. Drinking water is typically the largest source; other methods of fluoride therapy include fluoridation of toothpaste, salt, and milk. Water fluoridation, when feasible and culturally acceptable, has substantial advantages, especially for subgroups at high risk. In 1999 the U.S. Centers for Disease Control and Prevention listed water fluoridation as one of the ten great public health achievements of the 20th century; in contrast, most European countries have experienced substantial declines in tooth decay without its use, primarily due to the introduction of fluoride toothpaste in the 1970s. Fluoridation may be more justified in the U.S. because of socioeconomic inequalities in dental health and dental care. Public water fluoridation was first practiced in the U.S., and has been introduced to many other countries to varying degrees, with many countries having water that is naturally fluoridated to recommended levels and others, such as in Europe, using fluoridated salts as an alternative source of fluoride.