	Introduction

The fluoridation of drinking water often generates both strong support and opposition within communities. The practice is recommended by the U.S. Department of Health and Human Services (HHS) to prevent tooth decay. The decision to fluoridate a public water supply is made by the state or local municipality and is not mandated by any federal agency. Opponents have expressed concern regarding potential adverse health effects of exposure to fluoride, and some view the practice as an undemocratic infringement on individual freedom. The medical and public health communities generally have supported water fluoridation, citing it as a safe, effective, and equitable way to provide dental health protection community-wide. With the increased use of products containing fluoride, such as toothpaste and rinses, questions have emerged as to whether current fluoridation practices and levels are necessary and offer the most appropriate way to provide the beneficial effects of fluoride while avoiding adverse effects (such as tooth mottling or dental fluorosis) that can result from exposure to too much fluoride. Moreover, research gaps regarding the potential health effects of exposure to increased amounts of fluoride and among different age groups continue to add controversy to decisions regarding water fluoridation. Although many communities add fluoride to drinking water to strengthen teeth, others must treat their water to remove excess amounts of fluoride, which often is present naturally in water. The Environmental Protection Agency (EPA) regulates the maximum amount of fluoride that may be present in public drinking water supplies to protect against certain adverse health effects. In 1986, EPA issued a drinking water regulation for fluoride that includes an enforceable standard (a maximum contaminant level, or MCL) and a non-enforceable health-based maximum contaminant level goal (MCLG) of 4 milligrams per liter (mg/L) to protect against adverse effects on bone structure. EPA acknowledged that the standard did not protect infants and young children against dental fluorosis, which EPA considered a cosmetic effect rather than a health effect. To address concerns, EPA included in the regulation a secondary (advisory) standard of 2 mg/L to protect children against dental fluorosis and adverse health effects. As part of its ongoing review of the fluoride regulation, EPA asked the National Research Council (NRC) of the National Academy of Sciences to review the health risk data for fluoride and to assess the adequacy of EPA's standards. On March 22, 2006, NRC released its study and concluded that EPA's 4 mg/L MCLG should be lowered. It also discusses the regulation of fluoride in drinking water to protect against adverse health effects from exposure to higher levels of fluoride, and it reviews the status of federal efforts to update the health risk assessment for fluoride and the primary drinking water standard for fluoride. In 2010, CDC reported that more than 204.2 million (73.9%) of the people in the United States who received their water from public water systems received fluoridated water. One of CDC's national health goals is to increase the proportion of the U.S. population served by community water systems with "optimally" fluoridated drinking water to 79.6% by 2020. To make a determination to revise the standard, EPA must not only review scientific information, but also must evaluate analytical methods for testing for fluoride at lower levels, treatment feasibility (including cost), occurrence, and exposure. In 2011, HHS proposed that community water systems use a fluoridation level of 0.7 milligrams per liter, which is the lower end of the current recommended range of 0.7 mg/L to 1.2 mg/L.
According to the Centers for Disease Control and Prevention (CDC), in 2010, 73.9% of the people in the United States who receive their water from a public water system received fluoridated water (roughly 204.3 million people). One of CDC's national health goals is to increase the proportion of the U.S. population served by community water systems with "optimally" fluoridated drinking water to 79.6% by 2020. The decision to add fluoride to a water supply is made by local or state governments. The Department of Health and Human Services (HHS) had long recommended an optimal fluoridation level in the range of 0.7 to 1.2 milligrams per liter (mg/L) to prevent tooth decay.
The fluoridation of drinking water often generates both strong support and opposition within communities. This practice is controversial because fluoride has been found to have beneficial effects at low levels and is intentionally added to many public water supplies; however, at higher concentrations, it is known to have toxic effects. The Environmental Protection Agency (EPA) regulates the amount of fluoride that may be present in public water supplies to protect against fluoride's adverse health effects. Fluoridation opponents have expressed concern regarding potential adverse health effects of fluoride ingestion, and some view the practice as an unjustified infringement on individual freedom. The medical and public health communities generally have recommended water fluoridation, citing it as a safe, effective, and equitable way to provide dental health protection community-wide.
Because the use of fluoridated dental products and the consumption of food and beverages made with fluoridated water have increased since HHS recommended optimal levels for fluoridation, many people now may be exposed to more fluoride than had been anticipated. Consequently, questions have emerged as to whether current water fluoridation practices and levels offer the most appropriate ways to provide the expected beneficial effects of fluoride while avoiding adverse effects (most commonly, tooth mottling or pitting—dental fluorosis) that may result from ingestion of too much fluoride when teeth are developing. Also, scientific uncertainty regarding the health effects of exposure to higher levels of fluoride adds controversy to decisions regarding water fluoridation. In 2011, HHS proposed to reduce the recommended level to 0.7 mg/L.
Although fluoride is added to water to strengthen teeth, some communities must treat their water to remove excess amounts of fluoride that is present either naturally or from pollution. In 1986, EPA issued a drinking water regulation for fluoride that includes an enforceable standard—a maximum contaminant level (MCL)—and an MCL goal (MCLG) of 4 mg/L to protect against adverse effects on bone structure. EPA acknowledged that the standard did not protect infants and young children against dental fluorosis, which EPA considered a cosmetic effect rather than a health effect. To address this concern, EPA included in the regulation a secondary (advisory) standard of 2 mg/L to protect children against dental fluorosis and adverse health effects. As part of its current review of the fluoride regulation, EPA asked the National Research Council (NRC) to review the health risk data for fluoride and to assess the adequacy of EPA's standards. In March 2006, NRC released its study and concluded that EPA's 4 mg/L MCLG should be lowered.
In 2011, EPA released new risk and exposure assessments for fluoride. The agency announced its intent to use this science and additional research to review the primary and secondary drinking water standards for fluoride and to determine whether to revise them. To make a regulatory determination, EPA also must consider analytical methods for testing for fluoride at lower concentrations, treatment feasibility (including cost), occurrence, and exposure.