water fluoridation water fluoridation 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. 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 $1.17 per person-year. defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. 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. bottled water typically has unknown fluoride levels. fluoridation does not affect the appearance, taste or smell of drinking water. tooth decay remains a major public health concern in most industrialized countries, affecting 60–90% of schoolchildren and the vast majority of adults. water fluoridation reduces cavities in children, while efficacy in adults is less clear. 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. however, this was based on older studies which failed to control for numerous variables, such as increasing sugar consumption as well as other dental strategies. most european countries have experienced substantial declines in tooth decay, though milk and salt fluoridation is widespread in lieu of water fluoridation. recent 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. although fluoridation can cause dental fluorosis, which can alter the appearance of developing teeth or enamel fluorosis, the differences are mild and usually not an aesthetic or public health concern. there is no clear evidence of other side effects from water fluoridation. 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. 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. the world health organization reports that water fluoridation, when feasible and culturally acceptable, has substantial advantages, especially for subgroups at high risk, while the european commission finds no benefit to water fluoridation compared with topical use. public water fluoridation was first practiced in the u.s. as of 2012, 25 countries have artificial water fluoridation to varying degrees, 11 of them have more than 50% of their population drinking fluoridated water. a further 28 countries have water that is naturally fluoridated, though in many of them the fluoride is above the optimal level. as of 2012, about 435 million people worldwide received water fluoridated at the recommended level (i.e., about 5.4% of the global population).: 56 about 214 million of them live in the united states. major health organizations such as the world health organization and fdi world dental federation supported water fluoridation as safe and effective. the centers for disease control and prevention lists water fluoridation as one of the ten great public health achievements of the 20th century in the u.s. despite this, the practice is controversial as a public health measure. some countries and communities have discontinued fluoridation, while others have expanded it. opponents of the practice argue that neither the benefits nor the risks have been studied adequately, and debate the conflict between what might be considered mass medication and individual liberties. goal a cavity starts in a tooth's outer enamel and spreads to the dentin and pulp inside. the goal of water fluoridation is to prevent tooth decay by adjusting the concentration of fluoride in public water supplies. tooth decay (dental caries) 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. 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 fluoride monitor (at left) in a community water tower pumphouse, minnesota, 1987 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 (naf) 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 (h2sif6) 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 (na2sif6) 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. these compounds were chosen for their solubility, safety, availability, and low cost. a 1992 census found that, for u.s. public water supply systems reporting the type of compound used, 63% of the population received water fluoridated with fluorosilicic acid, 28% with sodium fluorosilicate, and 9% with sodium fluoride. recommendations 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. although fluoride was once considered an essential nutrient, the u.s. national research council has since 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. the european food safety authority's panel on dietetic products, nutrition and allergies (nda) 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 (ai) value for it. the ai of fluoride from all sources (including non-dietary sources) is 0.05 mg/kg body weight per day for both children and adults, including pregnant and lactating women. in 2011, the u.s. department of health and human services (hhs) and the u.s. environmental protection agency (epa) lowered the recommended level of fluoride to 0.7 mg/l. in 2015, the u.s. food and drug administration (fda), based on the recommendation of the u.s. public health service (phs) 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 (mg/l; equivalent to parts per million). previous recommendations were based on evaluations from 1962, when the u.s. specified the optimal level of fluoride 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. these standards are not appropriate for all parts of the world, where fluoride levels might be excessive and fluoride should be removed from water, and is based on assumptions that have become obsolete with the rise of air conditioning and increased use of soft drinks, processed food, fluoridated toothpaste, and other sources of fluorides. in 2011, the world health organization stated that 1.5 mg/l should be an absolute upper bound and that 0.5 mg/l may be an appropriate lower limit. a 2007 australian systematic review recommended a range from 0.6 to 1.1 mg/l. geographical areas associated with groundwater having over 1.5 mg/l of naturally occurring fluoride, which is above recommended levels. detail of southern arizona. areas in darker blues have groundwater with over 2 mg/l of naturally occurring fluoride. 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 (mgf+) being the next most common. because fluoride levels in water are usually controlled by the solubility of fluorite (caf2), high natural fluoride levels are associated with calcium-deficient, alkaline, and soft waters. 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. 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. 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 fda 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. evidence existing evidence suggests that water fluoridation reduces tooth decay. consistent evidence also suggests that it causes dental fluorosis, most of which is mild and not usually of aesthetic concern. no clear evidence of other adverse effects exists, though almost all research thereof has been of poor quality. effectiveness reviews have shown that water fluoridation reduces cavities in children. a conclusion for the efficacy in adults is less clear with some reviews finding benefit and others not. studies in the u.s. in the 1950s and 1960s showed that water fluoridation reduced childhood cavities by fifty to sixty percent, while studies in 1989 and 1990 showed lower reductions (40% and 18% respectively), likely due to increasing use of fluoride from other sources, notably toothpaste, and also the 'halo effect'