Water fluoridation
Water fluoridation is the controlled addition of fluoride to public water supplies to reduce tooth decay. Fluoridated water maintains fluoride levels effective for cavity prevention, achieved naturally or through supplementation. In the mouth, fluoride slows tooth enamel demineralization and enhances remineralization in early-stage cavities. Defluoridation is necessary when natural fluoride exceeds recommended limits. The World Health Organization recommends fluoride levels of 0.5–1.5 mg/L, depending on climate and other factors. In the U.S., the recommended level has been 0.7 mg/L since 2015, lowered from 1.2 mg/L. Bottled water often has unknown fluoride levels.
Tooth decay affects 60–90% of schoolchildren worldwide. Fluoridation reduces cavities in children, with Cochrane reviews estimating reductions of 35% in baby teeth and 26% in permanent teeth when no other fluoride sources are available, though efficacy in adults is less clear. In Europe and other regions, declining decay rates are attributed to topical fluorides and alternatives like salt fluoridation and nano-hydroxyapatite.
The United States was the first country to engage in water fluoridation, and 72% of its population drinks fluoridated water as of 2022. Globally, 5.4% of people receive fluoridated water, though its use remains rare in Europe, except in Ireland and parts of Spain. The WHO, FDI World Dental Federation, and the United States' Centers for Disease Control and Prevention endorse fluoridation as safe and effective at recommended levels. Critics question its risks, efficacy, and ethical implications.
Goal
The goal of water fluoridation is to prevent tooth decay by adjusting the concentration of fluoride in public water supplies. Tooth decay is one of the most prevalent chronic diseases worldwide. Although it is rarely life-threatening, tooth decay can cause pain and impair eating, speaking, facial appearance, and acceptance into society, and it greatly affects the quality of life of children, particularly those of low socioeconomic status. In most industrialized countries, tooth decay affects 60–90% of schoolchildren and the vast majority of adults; although the problem appears to be less in Africa's developing countries, it is expected to increase in several countries there because of changing diet and inadequate fluoride exposure. In the U.S., minorities and the poor both have higher rates of decayed and missing teeth, and their children have less dental care. Once a cavity occurs, the tooth's fate is that of repeated restorations, with estimates for the median life of an amalgam tooth filling ranging from 9 to 14 years. Oral disease is the fourth most expensive disease to treat. The motivation for fluoridation of salt or water is similar to that of iodized salt for the prevention of congenital hypothyroidism and goiter.The goal of water fluoridation is to prevent a chronic disease whose burdens particularly fall on children and the poor. Another of the goals was to bridge inequalities in dental health and dental care. Some studies suggest that fluoridation reduces oral health inequalities between the rich and poor, but the evidence is limited. There is anecdotal but not scientific evidence that fluoride allows more time for dental treatment by slowing the progression of tooth decay, and that it simplifies treatment by causing most cavities to occur in pits and fissures of teeth. Other reviews have found not enough evidence to determine if water fluoridation reduces oral-health social disparities.
Health and dental organizations worldwide have endorsed its safety and effectiveness at recommended levels. Its use began in 1945, following studies of children in a region where higher levels of fluoride occur naturally in the water. Further research showed that moderate fluoridation prevents tooth decay.
Implementation
Fluoridation does not affect the appearance, taste, or smell of drinking water. It is normally accomplished by adding one of three compounds to the water: sodium fluoride, fluorosilicic acid, or sodium fluorosilicate.- Sodium fluoride was the first compound used and is the reference standard. It is a white, odorless powder or crystal; the crystalline form is preferred if manual handling is used, as it minimizes dust. It is more expensive than the other compounds, but is easily handled and is usually used by smaller utility companies. It is toxic in gram quantities by ingestion or inhalation.
- Fluorosilicic acid is the most commonly used additive for water fluoridation in the United States. It is an inexpensive liquid by-product of phosphate fertilizer manufacture. It comes in varying strengths, typically 23–25%; because it contains so much water, shipping can be expensive. It is also known as hexafluorosilicic, hexafluosilicic, hydrofluosilicic, and silicofluoric acid.
- Sodium fluorosilicate is the sodium salt of fluorosilicic acid. It is a powder or very fine crystal that is easier to ship than fluorosilicic acid. It is also known as sodium silicofluoride.
Occurrences
Fluoride naturally occurring in water can be above, at, or below recommended levels. Rivers and lakes generally contain fluoride levels less than 0.5 mg/L, but groundwater, particularly in volcanic or mountainous areas, can contain as much as 50 mg/L. Higher concentrations of fluorine are found in alkaline volcanic, hydrothermal, sedimentary, and other rocks derived from highly evolved magmas and hydrothermal solutions, and this fluorine dissolves into nearby water as fluoride. In most drinking waters, over 95% of total fluoride is the F− ion, with the magnesium–fluoride complex being the next most common. Because fluoride levels in water are usually controlled by the solubility of fluorite, high natural fluoride levels are associated with calcium-deficient, alkaline, and soft waters.Some bottled waters contain undeclared fluoride, which can be present naturally in source waters, or if water is sourced from a public supply which has been fluoridated. The United States Food and Drug Administration states that bottled water products labeled as de-ionized, purified, demineralized, or distilled have been treated in such a way that they contain no or only trace amounts of fluoride, unless they specifically list fluoride as an added ingredient.
Recommendations
Target level
Authorities such as the World Health Organization publish recommendations for the amount of fluoride in piped water. The lower bound is set to reduce the incidence of dental caries and the upper bound is set to prevent harms such dental fluorosis. Levels below this range can be increased by water fluoridation and levels above this range should be reduced using treatment technology. The WHO upper limit of 1.5 mg/L has been repeatedly reaffirmed since 1984. The WHO mentions that the upper limit may need to be reduced in setting some national standards to keep the consumption below 6 mg/day. This can happen in case of higher piped water consumption such as in warmer climates, or when other sources of fluoride are present. In 2011, the WHO reports that protection against dental caries begin at 0.5 mg/L and that most fluoridation standards target a range of 0.5-1.0 mg/L. The WHO itself does not give a target for fluoridation.The European Food Safety Authority's Panel on Dietetic Products, Nutrition and Allergies considers fluoride not to be an essential nutrient, yet, due to the beneficial effects of dietary fluoride on prevention of dental caries they have defined an Adequate Intake value for it. The AI of fluoride from all sources is 0.05 mg/kg body weight per day for both children and adults, including pregnant and lactating women. Applying the 60 kg adult assumption, this is equivalent to 3 mg/day. The EFSA has an upper legal limit for fluoride content in water at 1.5 mg/L. In 2024 it prepared a draft for the tolerable upper intake levels for daily fluoride consumption in children.
In 2011, the U.S. Department of Health and Human Services and the U.S. Environmental Protection Agency lowered the recommended level of fluoride to 0.7 mg/L. In 2015, the U.S. FDA, based on the recommendation of the U.S. Public Health Service for fluoridation of community water systems, recommended that bottled water manufacturers limit fluoride in bottled water to no more than 0.7 milligrams per liter.
A 2007 Australian systematic review recommended a range from 0.6 to 1.1 mg/L.
Historical USA recommendations
Pre-2011 US recommendations were based on evaluations from 1962, when the U.S. specified the optimal level of fluoride in water to range from 0.7 to 1.2 mg/L, depending on the average maximum daily air temperature; the optimal level is lower in warmer climates, where people drink more water, and is higher in cooler climates.Between 1974 and 1989, fluoride was listed as an essential nutrient by the U.S. National Research Council. In 1989, it removed this designation due to the lack of studies showing it is essential for human growth, though still considering fluoride a "beneficial element" due to its positive impact on oral health. Studies in the late 1980s and the early 1990s indicate that childhood fluoride intake is around 0.05 mg/kg body weight per day when fluoridated and 0.03 mg/kg/day when not.
Methods to reach target level
In the United States, the Centers for Disease Control and Prevention developed recommendations for water fluoridation that specify requirements for personnel, reporting, training, inspection, monitoring, surveillance, and actions in case of overfeed, along with technical requirements for each major compound used.The WHO recommends reaching the adequate level of fluoride intake through fluoridation of low fluoride water as well as topical fluoride preparations including fluoridated toothpastes, silver diamine fluoride varnish, and glass ionomer cement. The WHO also recommends that excess intake be avoided by switching to an alternative water source if possible, or through defluoridating techniques.
Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. It can be accomplished by percolating water through granular beds of activated alumina, bone meal, bone char, or tricalcium phosphate; by coagulation with alum; or by precipitation with lime. Clay can also be used for defluoridation, but one must first ensure it contains no toxic chemicals or other pollutants.
Pitcher or faucet-mounted water filters do not alter fluoride content; the more-expensive reverse osmosis filters remove 65–95% of fluoride, and distillation removes all fluoride.