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Water fluoridation


Water fluoridation is the controlled addition of fluoride to a public water supply in order to reduce tooth decay. Its use in the U.S. began in the 1940s, following studies of children in a region where water is naturally fluoridated. Too much fluoridation causes dental fluorosis, which mottles or stains teeth, but U.S. researchers discovered that moderate fluoridation prevents cavities, and it is now used for about two-thirds of the U.S. population on public water systems and for about 5.7 percent of people worldwide. Although there is no clear evidence of adverse effects other than fluorosis, most of which is mild and not of aesthetic concern, water fluoridation has been contentious for ethical, safety, and efficacy reasons, and opposition to water fluoridation exists despite its support by public health organizations.


The goal of water fluoridation is to prevent tooth decay (dental caries), one of the most prevalent chronic diseases worldwide, and one that greatly affects the quality of life of children, particularly those of low socioeconomic status. Fluoride toothpaste, dental sealants, and other techniques are also effective in preventing tooth decay.1 Water fluoridation, when culturally acceptable and technically feasible, is said to have substantial advantages over toothpaste, especially for subgroups at high risk.2


Fluoride monitor (at left) in a community water tower pumphouse, Minnesota, 1987.

Fluoridation is normally accomplished by adding one of three compounds to drinking water:

  • Hydrofluosilicic acid (H2SiF6; also known as hexafluorosilicic, hexafluosilicic, silicofluoric, or fluosilicic acid), is an inexpensive watery byproduct of phosphate fertilizer manufacture.3
  • Sodium silicofluoride (Na2SiF6) is a powder that is easier to ship than hydrofluosilicic acid.3
  • Sodium fluoride (NaF), the first compound used, is the reference standard.3 It is more expensive, but is easily handled and is used by smaller utility companies.4

These compounds were chosen for their solubility, safety, availability, and low cost.3 The estimated cost of fluoridation in the U.S., in 1999 dollars, is $0.72 per person per year (range: $0.17-$7.62); larger water systems have lower per capita cost, and the cost is also affected by the number of fluoride injection points in the water system, the type of feeder and monitoring equipment, the fluoride chemical and its transportation and storage, and water plant personnel expertise.5 A 1992 census found that, for U.S. public water supply systems reporting the type of compound used, 63 percent of the population received water fluoridated with hydrofluosilicic acid, 28 percent with sodium silicofluoride, and 9 percent with sodium fluoride.6

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.7

In the U.S. the optimal level of fluoridation ranges from 0.7 to 1.2 mg/L (milligrams per liter, equivalent to parts per million), 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.8 In Australia optimal levels range from 0.6 to 1.1 mg/L.9 Some water is naturally fluoridated at optimal levels, and requires neither fluoridation nor defluoridation.7


Water fluoridation operates by creating low levels (about 0.04 mg/L) of fluoride in saliva and plaque fluid. This in turn reduces the rate of tooth enamel demineralization, and increases the rate of remineralization of the early stages of cavities.10 Fluoride is the only agent that has a strong effect on cavities; technically, it does not prevent cavities but rather controls the rate at which they develop.11

Evidence basis

Existing evidence strongly suggests that water fluoridation prevents tooth decay. There is also consistent evidence that it causes fluorosis, most of which is mild and not considered to be of aesthetic concern.9 The best available evidence shows no association with other adverse effects. However, the quality of the research on fluoridation has been generally low.12


Water fluoridation is the most effective and socially equitable way to achieve wide exposure to fluoride's cavity-prevention effects,9 and has contributed to dental health worldwide of children and adults.5 A 2000 systematic review found that fluoridation was associated with a decreased proportion of children with cavities (the median of mean decreases was 14.6 percent, the range −5 percent to 64 percent), and with a decrease in decayed, missing, and filled primary teeth (the median of mean decreases was 2.25 teeth, the range 0.5 to 4.4 teeth). The evidence was of moderate quality. Many studies did not attempt to reduce observer bias, control for confounding factors, or use appropriate analysis.12 Fluoridation also prevents cavities in adults of all ages; 13 a 2007 meta-analysis found that fluoridation prevented an estimated 27 percent of cavities in adults (range 19 percent-34 percent).14

The decline in tooth decay in the U.S. since water fluoridation began in the 1950s has been attributed largely to the fluoridation,8 and has been listed as one of the ten great public health achievements of the twentieth century in the U.S.15 Initial studies showed that water fluoridation led to reductions of 50-60 percent in childhood cavities; more recent estimates are lower (18-40 percent), likely due to increasing use of fluoride from other sources, notably toothpaste.5 The introduction of fluoride toothpaste in the early 1970s has been the main reason for the decline in tooth decay since then in industrialized countries.10

In Europe, most countries have experienced substantial declines in cavities without the use of water fluoridation, indicating that water fluoridation may be unnecessary in industrialized countries.10 For example, in Finland and Germany, tooth decay rates remained stable or continued to decline after water fluoridation stopped. Fluoridation may be more justified in the U.S. because unlike most European countries, the U.S. does not have school-based dental care, many children do not attend a dentist regularly, and for many U.S. children water fluoridation is the prime source of exposure to fluoride.16

Although a 1989 workshop on cost effectiveness of caries prevention concluded that water fluoridation is one of the few public health measures that saves more money than it costs, little high-quality research has been done on the cost-effectiveness and solid data are scarce.58


At the commonly recommended dosage, the only clear adverse effect is dental fluorosis, most of which is mild and not considered to be of aesthetic concern. Compared to unfluoridated water, fluoridation to 1 mg/L is estimated to cause fluorosis in one of every 6 people, and to cause fluorosis of aesthetic concern in one of every 22 people.12 Fluoridation has little effect on risk of bone fracture (broken bones); it may result in slightly lower fracture risk than either excessively high levels of fluoridation or no fluoridation.9 There is no clear association between fluoridation and cancer, deaths due to cancer, bone cancer, or osteosarcoma.9

In rare cases improper implementation of water fluoridation can result in overfluoridation, resulting in fluoride poisoning. For example, in Hooper Bay, Alaska in 1992, a combination of equipment and human errors resulted in one of the two village wells being overfluoridated, causing one death and an estimated 295 nonfatal cases of fluoride intoxication.17

Adverse effects that lack sufficient evidence to reach a scientific conclusion9 include:

  • Like other common water additives such as chlorine, hydrofluosilicic acid and sodium silicofluoride decrease pH, and cause a small increase of corrosivity; this can easily be resolved by adjusting the pH upward.18
  • Some reports have linked hydrofluosilicic acid and sodium silicofluoride to increased human lead uptake;19 these have been criticized as providing no credible evidence.18
  • Arsenic and lead may be present in fluoride compounds added to water, but there is no credible evidence that this is of concern: concentrations are below measurement limits.18

The effect of water fluoridation on the environment has been investigated, and no adverse effects have been established. Issues studied have included fluoride concentrations in groundwater and downstream rivers; lawns, gardens, and plants; consumption of plants grown in fluoridated water; air emissions; and equipment noise.18


Almost all major health and dental organizations support water fluoridation, or have found no association between fluoridation and adverse effects.2021 These organizations include the World Health Organization,22 the Centers for Disease Control and Prevention,5 the U.S. Surgeon General,23 and the American Dental Association.24

Despite support by public health organizations and authorities, efforts to introduce water fluoridation meet considerable opposition whenever it is proposed.20 Controversies include disputes over fluoridation's benefits and the strength of the evidence basis for these benefits, the difficulty of identifying harms, legal issues over whether water fluoridation is a medicine, and the ethics of mass intervention.25 Opposition campaigns involve newspaper articles, talk radio, and public forums. Media reporters are often poorly equipped to explain the scientific issues, and are motivated to present controversy regardless of the underlying scientific merits. Internet websites, which are increasingly used by the public for health information, contain a wide range of material about fluoridation ranging from factual to fraudulent, with a disproportionate percentage opposed to fluoridation. Conspiracy theories involving fluoridation are common, and include claims that fluoridation is part of a Communist or New World Order plot to take over the world, that it was pioneered by a German chemical company to make people submissive to those in power, that it is backed by the sugar or aluminum or phosphate industries, or that it is a smokescreen to cover failure to provide dental care to the poor.20 Specific antifluoridation arguments change to match the spirit of the time.26

Use around the world

U.S. residents served with community water fluoridation, 1992 and 2006. The percentages are the proportions of the resident population served by public water supplies who are receiving fluoridated water.27

About 5.7 percent of people worldwide drink fluoridated water;25 this includes 61.5 percent of the U.S. population.28 12 million people in Western Europe have fluoridated water, mainly in England, Spain, and Ireland. France, Germany, and some other European countries use fluoridated salt instead; the Netherlands, Sweden, and a few other European countries rely on fluoride supplements and other measures.29 The justification for water fluoridation is analogous to the use of iodized salt for the prevention of goiters. China, Japan, the Philippines, and India do not fluoridate water.30

Australia, Brazil, Chile, Colombia, Canada, Hong Kong Special Administrative Region of China, Israel, Malaysia, and New Zealand have introduced water fluoridation to varying degrees. Germany, Finland, Japan, the Netherlands, Sweden, and Switzerland have discontinued water fluoridation schemes for reasons which are not systematically available.25

Alternative methods

Water fluoridation is one of several methods of fluoride therapy; others include fluoridation of salt, milk, and toothpaste.31

The effectiveness of salt fluoridation is about the same as water fluoridation, if most salt for human consumption is fluoridated. Fluoridated salt reaches the consumer in salt at home, in meals at school and at large kitchens, and in bread. For example, Jamaica has just one salt producer, but a complex public water supply; it fluoridated all salt starting in 1987, resulting in a notable decline in the prevalence of cavities. Universal salt fluoridation is also practiced in Columbia, Jamaica, and the Canton of Vaud in Switzerland; in France and Germany fluoridated salt is widely used in households but unfluoridated salt is also available. Concentrations of fluoride in salt range from 90 mg/kg to 350 mg/kg, with studies suggesting an optimal concentration of around 250 mg/kg.31

Milk fluoridation is being practiced by the Borrow Foundation in some parts of Bulgaria, Chile, Peru, Russia, Thailand and the United Kingdom. For example, milk-powder fluoridation is used in Chilean rural areas where water fluoridation is not technically feasible.32 These programs are aimed at children, and have neither targeted nor been evaluated for adults.31 A 2005 systematic review found insufficient evidence to support the practice, but also concluded that studies suggest that fluoridated milk benefits schoolchildren, especially their permanent teeth.33

Some dental professionals are concerned that the growing use of bottled water may decrease the amount of fluoride exposure people will receive.34 Some bottlers such as Danone have begun adding fluoride to their water.35 On April 17, 2007, 1 Medical News Today stated, "There is no correlation between the increased consumption of bottled water and an increase in cavities."36 In October 2006, the United States Food and Drug Administration issued a health claim notification permitting water bottlers to claim that fluoridated bottled water can promote oral health. The claims are not allowed to be made on bottled water marketed to infants.37


The history of water fluoridation can be divided into three periods. The first (c. 1901-1933) was research into the cause of a form of mottled tooth enamel called "Colorado brown stain," which later became known as fluorosis. The second (c. 1933-'945) focused on the relationship between fluoride concentrations, fluorosis, and tooth decay. The third period, from 1945 on, focused on adding fluoride to community water supplies.38

Colorado brown stain

Photograph of Dr. G.V. Black (left) and Drs. Isaac Burton and F. Y. Wilson, 1909, studying the "Colorado Brown Stain" (picture taken by McKay, printed in Douglas W.A.:"History of dentistry in Colorado, 1859-1959").

While the use of fluorides for prevention of dental caries (cavities) was discussed in the nineteenth century in Europe,39 community water fluoridation in the United States is partly due to the research of Dr. Frederick McKay, who pressed the dental community for an investigation into what was then known as "Colorado Brown Stain."40 The condition, now known as dental fluorosis, when in its severe form is characterized by cracking and pitting of the teeth.414243 Of 2,945 children examined in 1909 by Dr. McKay, 87.5 percent had some degree of stain or mottling. All the affected children were from the Pikes Peak region. Despite the negative impact on the physical appearance of their teeth, the children with stained, mottled and pitted teeth also had fewer cavities than other children. McKay brought this to the attention of Dr. G.V. Black, and Black's interest was followed by greater interest within the dental profession.

Initial hypotheses for the staining included poor nutrition, overconsumption of pork or milk, radium exposure, childhood diseases, or a calcium deficiency in the local drinking water.40 In 1931, researchers from the Aluminum Company of America (ALCOA) concluded that the cause of the Colorado stain was a high concentration of fluoride ions in the region's drinking water (ranging from 2 to 13.7 mg/L) and areas with lower concentrations had no staining (1 mg/L or less).44 Pikes Peak's rock formations contained the mineral cryolite, one of whose constituents is fluorine. As the rain and snow fell, the resulting runoff water dissolved fluoride which made its way into the water supply.

Dental and aluminum researchers then moved toward determining a relatively safe level of fluoride chemicals to be added to water supplies. The research had two goals: (1) to warn communities with a high concentration of fluoride of the danger, initiating a reduction of the fluoride levels in order to reduce incidences of fluorosis, and (2) to encourage communities with a low concentration of fluoride in drinking water to add fluoride chemicals in order to help prevent tooth decay. By 2006, 69.2 percent of the U.S. population on public water systems were receiving fluoridated water, amounting to 61.5 percent of the total U.S. population; 3.0 percent of the population on public water systems were receiving naturally occurring fluoride.28

Early studies

A study of varying amounts of fluoride in water was led by Dr. H. Trendley Dean, a dental officer of the U.S. Public Health Service.4546 In 1936 and 1937, Dr. Dean and other dentists compared statistics from Amarillo, which had 2.8 - 3.9 mg/L fluoride content, and low fluoride Wichita Falls. The data is alleged to show less cavities in Amarillo children, but the studies were never published.47 Dr. Dean's research on the fluoride-dental caries relationship, published in 1942, included 7,000 children from 21 cities in Colorado, Illinois, Indiana, and Ohio. The study concluded that the optimal amount of fluoride which minimized the risk of severe fluorosis but had positive benefits for tooth decay was 1 mg per day, per adult. Although fluoride is more abundant in the environment today, this was estimated to correlate with the concentration of 1 mg/L.

In 1937, dentists Henry Klein and Carroll E. Palmer had considered the possibility of fluoridation to prevent cavities after their evaluation of data gathered by a Public Health Service team at dental examinations of Native American children.48 In a series of papers published afterwards (1937-1941), yet disregarded by his colleagues within the U.S.P.H.S., Klein summarized his findings on tooth development in children and related problems in epidemiological investigations on caries prevalence.

In 1939, Dr. Gerald J. Cox49 conducted laboratory tests using rats that were fed aluminum and fluoride. Dr. Cox suggested adding fluoride to drinking water (or other media such as milk or bottled water) in order to improve oral health.50

In the mid 1940s, four widely cited studies were conducted. The researchers investigated cities that had both fluoridated and unfluoridated water. The first pair was Muskegon, Michigan and Grand Rapids, Michigan, making Grand Rapids the first community in the world to add fluoride chemicals to its drinking water to try to benefit dental health on January 25, 1945.51 Kingston, New York was paired with Newburgh, New York.52 Oak Park, Illinois was paired with Evanston, Illinois. Sarnia, Ontario was paired with Brantford, Ontario, Canada.53

In 1952 Nebraska Representative A.L. Miller complained that there had been no studies carried out to assess the potential adverse health risk to senior citizens, pregnant women or people with chronic diseases from exposure to the fluoridation chemicals.47 A decrease in the incidence of tooth decay was found in some of the cities which had added fluoride chemicals to water supplies. The early comparison studies would later be criticized as, "primitive," with a, "virtual absence of quantitative, statistical methods… nonrandom method of selecting data and… high sensitivity of the results to the way in which the study populations were grouped… " in the journal Nature.54

Opposition to water fluoridation

Opposition to water fluoridation refers to activism against the fluoridation of public water supplies. The controversy occurs mainly in English-speaking countries, as Continental Europe does not practice water fluoridation, although some continental countries fluoridate salt.55 Most of the health effects are associated with water fluoridation at levels above the recommended concentration of 0.7 - 1.2 mg/L (0.7 for hot climate, 1.2 in cool climates), but those organizations and individuals opposed raise concerns that the intake is not easily controlled, and that children, small individuals, and others may be more susceptible to health problems. Those opposed also argue that water fluoridation is ineffective,56 may cause serious health problems,575859 and imposes ethical issues.60 Opposition to fluoridation has existed since its initiation in the 1940s.55 During the 1950s and 1960s, some opponents of water fluoridation also put forward conspiracy theories describing fluoridation as a communist plot to undermine public health.61 Sociologists used to view opposition to water fluoridation as an example of misinformation. However, contemporary critiques of this position have pointed out that this position rests on an uncritical attitude toward scientific knowledge.55


Many who oppose water fluoridation consider it to be a form of compulsory mass medication. They argue that consent of all water consumers cannot be achieved, nor can water suppliers accurately control the exact levels of fluoride that individuals receive, nor monitor their response.60 It is also argued that, because of the negative health effects of fluoride exposure, mandatory fluoridation of public water supplies is a breach of ethics and a human rights violation.

In the United Kingdom the Green Party refers to fluoride as a poison, claim that water fluoridation violates Article 35 of the European Charter of Fundamental Rights, is banned by the UK poisons act of 1972, violates Articles 3 and 8 of the Human Rights Act and raises issues under the United Nations Convention on the Rights of the Child.62

Water fluoridation has also been criticized by Cross and Carton for violating the Nuremberg Code and the Council of Europe's Biomedical Convention of 1999.63 Dentistry professor David Locker and philosopher Howard Cohen argued that the moral status for advocating water fluoridation is "at best indeterminate" and could even be considered immoral because it infringes upon autonomy based on uncertain evidence, with possible negative effects.64

The precautionary principle

In an analysis published in the March 2006 issue of the Journal of Evidence Based Dental Practice, the authors examine the water fluoridation controversy in the context of the precautionary principle. The authors note that:

  • There are other ways of delivering fluoride besides the water supply;
  • Fluoride does not need to be swallowed to prevent tooth decay;
  • Tooth decay has dropped at the same rate in countries with, and without, water fluoridation;
  • People are now receiving fluoride from many other sources besides the water supply;
  • Studies indicate fluoride's potential to cause a wide range of adverse, systemic effects;
  • Since fluoridation affects so many people, “one might accept a lower level of proof before taking preventive actions.”65

Potential health risks

Health risks are generally associated with fluoride intake levels above the commonly recommended dosage, which is accomplished by fluoridating the water at 0.7 - 1.2 mg/L (0.7 for hot climates, 1.2 in cool climates). This was based on the assumption that adults consumes 2 L of water per day,66:345 but may a daily fluoride dose of between 1 - 3 mg/day, as men are recommended to drink 3 liters/day and women 2.2 liters/day.67 In 1986 the United States Environmental Protection Agency (EPA) established a maximum contaminant level (MCL) for fluoride at a concentration of 4 milligrams per liter (mg/L), which is the legal limit of fluoride allowed in the water. In 2006, a 12-person committee of the US National Research Council (NRC) reviewed the health risks associated with fluoride consumption66 and unanimously concluded that the maximum contaminant level of 4 mg/L should be lowered. The EPA has yet to act on the NRC's recommendation.6869 The limit was previously 1.4 - 2.4 mg/L, but it was raised to 4 mg/L in 1985.70

Opposition groups express the greatest concern for vulnerable populations, and the National Research Council states that children have a higher daily average intake than adults per kg of bodyweight.66:23 Those who work outside or have kidney problems will also drink more water. Of the following health problems, osteosarcoma, a rare bone disease affecting male children, is strictly associated with the recommended dosage of fluoride. The weight of the evidence does not support a relationship.71 However, a study performed as a doctoral thesis, which is described as the most rigorous yet by the Washington Post, found a relationship among young boys,72 but then the Harvard professor who advised the doctoral students determined that the results were not highly correlative enough to have evidentiary value; the professor then was investigated but exonerated by the federal government's Office of Research Integrity (ORI).73 An epidemiological connection between areas with high intake of silicofluorides and increased lead blood levels in children has been observed in areas fluoridated at the recommended dosage.7475 A 2007 update on this study confirmed the result and noted that silicofluorides, fluosilicic acid and sodium fluosilicate are used to fluoridate over 90 percent of US fluoridated municipal water supplies.76

Chemistry professor Paul Connett, the executive director of the Fluoride Action Network, points out that dosages cannot be controlled, so he believes that many of the health effects observed at levels above 1 mg/L are relevant for 1 mg/L. He highlights the issues raised by the 2006 report in the form uncertainties, data gaps, and a reduced margin of safety.77 A panel member of the report, Kathleen M. Thiessen, writes that the report does seem relevant to the debate, and that the "margin of safety between 1 mg/L and 4 mg/L is very low" because of the uncontrolled nature of the dosage.78 In her opinion fluoride intake should be minimized. Another panel member, Robert Isaacson, stated that "this report should be a wake-up call" and said that the possible effects on the endocrine gland and hormones are "something that I wouldn't want to happen to me if I had any say in the matter."79 John Dull, the chair of the panel, stated that "the thyroid changes worry me… we've gone with the status quo regarding fluoride for many years-for too long, really-and now we need to take a fresh look… I think that's why fluoridation is still being challenged so many years after it began. In the face of ignorance, controversy is rampant".57Hardy Limeback, another panel member, stated "the evidence that fluoridation is more harmful than beneficial is now overwhelming and policy makers who avoid thoroughly reviewing recent data before introducing new fluoridation schemes do so at risk of future litigation".80


In the past twenty years, a body of research has developed which indicates that the anticaries effects of fluoride on the teeth are largely derived from topical application (brushing) rather than systemic (swallowing).66:15-16 These findings are disputed by some researchers and public health agencies such