Water fluoridation involves adjusting the amount of fluoride naturally present in water. Fluoride is added to many communities’ drinking water when it falls below a certain concentration level. Community water that is fluoridated in this manner is monitored daily to ensure that proper levels of fluoridation are maintained.

The optimal range for fluoride levels in drinking water is between 0.7 to 1.2 parts per million (ppm) or milligrams per liter, according to the U.S. Public Health Service. Lower levels of this range are appropriate in warm-weather areas of the United States, and higher levels of this range apply to colder climates. This allows for the propensity of people in warm areas to drink more water than those in colder environments.

Fluoride was first added to community drinking water in the United States in 1945. Studies of its effects over a 15-year period found that fluoridated water reduced tooth decay in children by 60 percent.

Today, the people who use community water systems receive adequate levels of fluoride in the water. Fluoridated drinking water and beverages containing fluoride are the largest contributors to a person’s total consumption of fluoride. Children and adults alike benefit from the decay-preventing properties of fluoridated water.

Most people support water fluoridation. However, people who oppose it have questioned its safety and argued that it is a decision imposed upon them by others. The debate over whether or not to add fluoride to the water in some communities continues.

Water fluoridation has been determined to be a safe and effective method of preventing tooth decay by most major health and safety-related organizations. This includes the American Dental Association, the U.S. Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatric Dentistry. In October 2006, the U.S. Food and Drug Administration (FDA) approved the health claim "Drinking fluoridated water may reduce the risk of tooth decay" for use on bottled waters that contain between 0.6 and 1.0 milligrams per liter (mg/L) of total fluoride. However, this claim is not approved for bottle water products marketed specifically for use by infants.

Periodic assessments of drinking water regulations occur to ensure the safety of communities participating in water fluoridation programs.

For example, the Environmental Protection Agency (EPA) has set a maximum allowable level of fluoride in drinking water. Water is considered safe for drinking if fluoride levels do not exceed 4 ppm (although the optimal level in drinking water remains between 0.7 and 1.2 ppm). In 1993, the National Research Council (NRC) reported that the 4 ppm maximum was appropriate until additional studies could be performed.

In March 2006, the NRC recommended lowering the 4 ppm maximum. Its report included a finding that water with naturally occurring levels of fluoride above 2 ppm may cause dental fluorosis in children. This exposure may occur in communities that do not regulate fluoride levels in the water, or among those who rely on well water with naturally occurring high levels of fluoride. The NRC finding remains consistent with the established optimal level of fluoride (0.7 to 1.2 ppm) in public water systems.

Water fluoridation is considered a cost-effective method of delivering fluoride to all members of a community. The CDC recommends drinking fluoridated water in addition to using fluoride products on a regular basis (e.g., brushing teeth twice a day with a fluoride toothpaste) as part of a good dental hygiene program.