Community water fluoridation, hailed by the Centers for Disease Control and Prevention as one of the 20th century’s greatest public health interventions, has significantly reduced cavities and improved dental health in the U.S. since its inception in 1945.
This practice stemmed from observations in Colorado Springs in the early 1900s, where residents with brown-stained teeth, later linked to high fluoride levels, also had lower rates of tooth decay. Over the next several decades, research led by public health researchers confirmed that while excess fluoride caused cosmetic discoloration, lower fluoride concentrations prevented cavities without harmful side effects.
Early Fluoridation Trials
At the National Institutes of Health in the 1930s, Dr. H. Trendley Dean was investigating the epidemiology of dental fluorosis (generally white spots), a relatively new “condition” discovered in the early 1900s, but not understood reasonably well until the 1920s, according to Dr. Bruce A. Dye, Oral Health Equity chair of the Delta Dental of Colorado Foundation and professor of Dental Medicine at the University of Colorado Anschutz Medical Campus.
“Dean’s research was becoming focused on determining what levels of fluoride could be in drinking water before fluorosis would occur,” Dye says. “By the time World War II began, he determined that fluoride levels up to about 1.0 ppm in drinking water would not cause dental fluorosis in most people.”
In 1942, Dean’s 21 Cities Study found 7,200 young people living in 21 cities in Colorado, Illinois, Indiana and Ohio had fewer cavities and less severe decay when their community water supply was fluoridated. The effect leveled off when fluoride concentrations were greater than 1.0 ppm.
The first major trial of water fluoridation to a community water supply began in 1945 in Grand Rapids, Michigan, where dental exams soon confirmed that children who drank fluoridated water from birth had significantly fewer cavities.
The trial was part of a 15-year trial in partnership with the U.S. Public Health Service, U.S. Surgeon General, Michigan Department of Health, and the University of Michigan School of Dentistry.
“Grand Rapids was selected because the area was generally free of naturally occurring fluoride, and there were significant numbers of school-age children living in the area,” Dye says. “Muskegon was a neighboring city with similar characteristics that was selected as the control.”
An additional six cities were soon added to the community fluoridation trials.
Widespread Adoption
The initial decision to add fluoride to community water supplies also goes back to a significant problem observed during World War II, according to Dye.
In 1948, President Harry S. Truman signed the National Dental Research Act, establishing the National Institute of Dental Research at the NIH. The act was in response to the fact that more than 20 percent of young men drafted for military service were rejected due to dental issues—mostly cavities, says Dye. “The act called for increased dental research to address post-war concerns that military readiness would continue to be significantly affected by dental disease and the workforce would be unable to meet increasing treatment needs.”
Dean was named the first director of the NIDR and, according to Dye, quickly brought the federal agency in to support the Grand Rapids study. After five years, the benefits of fluoridation on reducing tooth decay were clear. After 10 years, cavity rates were reduced by more than 60 percent among the children in Grand Rapids, Dye says.
Following this success, more and more state and local governments began programs to fluoridate water nationwide, reaching over 200 million Americans by 2010. Today, about 77 percent of Americans have fluoridated water in their public water systems, according to the CDC.
How Fluoridated Water Works
Fluoride occurs naturally in most water, according to the CDC, but often at levels too low to prevent decay. Adjusting the concentration to the recommended 0.7 milligrams per liter—about three drops of water in a 55-gallon barrel—provides enough fluoride to strengthen tooth enamel.
The CDC adds that state and local governments choose to fluoridate their water, with the decision often going to the voters.
“Some states have laws that require water systems of a certain size to provide fluoridated water,” the agency states on its website. “In some areas, the level of naturally occurring fluoride in water is already at a level proven to prevent cavities. Community water systems add fluoride as needed to reach the optimal level. Communities also might remove fluoride if the natural level is too high.”
Research shows drinking fluoridated water results in a 25 percent reduction in cavities, leading to fewer dental issues, less pain, and fewer missed school and work days, according to the CDC. Financially, the agency adds, community water fluoridation is cost-effective: for every dollar spent, communities of 1,000 or more people save an estimated $20 in dental treatment costs.
“In the 1950s, almost all children and adults experienced tooth decay, and many experienced severe [tooth decay],” Dye says. “It was a major public health problem in the U.S. In 1960, 50 percent of all adults aged 65 were edentulous (having no natural teeth). Water fluoridation has played a very important role in helping to reduce the prevalence of complete tooth loss from 50 percent to close to 10 percent today.”
In 2015, Dye adds, the U.S. Public Health Service adjusted the fluoride guidelines for public water supplies to a concentration of 0.7 ppm because of the widespread availability of fluoride in oral care products, such as toothpaste and rinses, and in drinking water.
Concerns and Controversies
The American Dental Association “unreservedly” endorses fluoridating community water supplies. “The ADA actively advocates for the fluoridation of public water supplies as an effective way to prevent tooth decay and promote oral health,” its website states.
And while most municipalities and local governments fluoridate their water supplies, Dye says concerns surrounding the practice include the notion that too much fluoride can cause health problems such as increased bone fractures, arthritis and some cancers, namely osteosarcoma.
“The more recent concerns have been around neurotoxicity and cognitive problems affecting children,” he says. Some recent studies suggest that excess exposure to fluoride—at levels more than twice the recommended level—could harm developing brains.
An August 2024 National Toxicology Program report on the association between fluoride exposure and neurodevelopment and cognition concluded that higher levels of environmental fluoride exposure—more than 1.5 ppm—were associated with lower IQ in children. Dye points out that current water fluoridation guidelines call for significantly lower levels of 0.7 ppm.
Some local governments, including in Florida, North Carolina, Pennsylvania, Alaska and Texas, have removed fluoride from drinking water, citing health concerns and personal choice. A 2022 University of Calgary study showed increases in tooth decay procedures in Calgary, Canada, and Juneau, Alaska, after each city ended water fluoridation.
In other places, residents have agitated when fluoride was removed from drinking water. In Buffalo New York, locals filed a class-action lawsuit in 2023 against the city after it ended fluoridation without informing residents. One Buffalo mother said her 10-year-old son experienced oral health problems from a lack of fluoride. Fluoride was added back to Buffalo's water in September 2024.
“The bottom line is that the National Toxicology Program report and other recent systematic reviews indicate that the level of fluoride used in community water fluoridation is effective for preventing tooth decay and is not associated with any change in people’s IQ or neurological development,” Scott Tomar, a member of the National Fluoridation Advisory Committee, concluded in an August 2024 statement.
