Fluoride in drinking water has become a highly charged topic in recent weeks. In March, Utah became the first state to prohibit the addition of fluoride to the state’s public water systems, a move praised by U.S. Health Secretary Robert F. Kennedy. However, some health groups are raising the alarm.

The American Dental Association continues to push for water fluoridation, saying a ban on the practice would hurt people, cost money and eventually harm the economy.

Tao Wen is an assistant professor in the Department of Earth and Environmental Sciences in Syracuse University’s College of Arts and Sciences. His research specialties include water sustainability and the connection between energy, agriculture, urbanization and water quality. Professor Wen answered four questions about the use of fluoride in public drinking water, discussing how his research group studies water quality.

Q: What are some general facts people should know about the use of fluoride in public water?

A: In general, you don’t want too much or too little fluoride in drinking water, including the water provided through the public water system. Too little fluoride in drinking water can cause tooth cavities.

Fluoride is added to many public water systems in the U.S. to help prevent tooth decay. This practice, known as community water fluoridation, has been endorsed by numerous health organizations for its dental health benefits. Too much fluoride in drinking water can contribute to dental and skeletal fluorosis.

It is important to note that not all drinking water systems are fluoridated. Fluoride in water can come from different sources. Generally, it can occur naturally, particularly in certain geological settings and/or originate from human sources.

Q: What is considered a ‘safe’ amount of fluoride? What are signs or indicators that there is an unsafe amount in a water source?

A: The U.S. Public Health Service recommends an optimal fluoride concentration of 0.7 mg/L to balance the benefits of cavity prevention with the risk of dental fluorosis—a cosmetic condition caused by excessive fluoride exposure during tooth development. The U.S. Environmental Protection Agency (EPA) sets an enforceable Maximum Contaminant Level (MCL) of 4.0 mg/L to protect against skeletal fluorosis, a bone disease that can result from prolonged exposure to high fluoride levels.

In addition, the EPA has a secondary (non-enforceable) standard of 2.0 mg/L to reduce the risk of dental fluorosis in children. The only accurate way to determine fluoride levels in water is through laboratory testing. Individuals can have their private well water tested or consult their local public water supplier for current water quality reports.

In some cases, signs of fluoride exposure may include cosmetic changes in teeth, such as white streaks or mottling. A recent study identified several key factors that influence fluoride concentrations in groundwater: pH, total dissolved solids, alkalinity, well depth, water temperature, Ca/Na ratio, mean annual precipitation, and aquifer lithology.

Understanding these factors can help infer potential fluoride levels in groundwater, particularly in regions where direct testing is not readily available.

Q: In your own research, what do you study or look for as it relates to fluoride in your water samples?

A: My research group broadly studies water quality in groundwater and surface water across urban, rural, and natural settings. In one of our recent studies, we monitored surface water quality in an urban watershed in the City of Syracuse to assess the impact of various human infrastructures—including cemeteries—on solute concentrations. Fluoride was among several ions we tracked.

Among the 286 stream water samples collected from February 2022 to January 2023, we did not observe any fluoride concentrations exceeding the EPA’s secondary standard of 2 mg/L. Although our primary focus was on nitrate, we found no significant increase in fluoride concentration downstream of the cemetery.

This suggests that burial decay products, which could potentially contribute fluoride, were not a dominant source in our study area. Instead, the data suggest that fluoride concentrations varied with river flow and may be influenced by natural (geogenic) sources, among other possible sources.

Q: In your academic opinion, why do you think there continues to be this focus on fluoride in drinking water?

A: Fluoride remains a topic of public interest and debate for several reasons. First and foremost, it is one of the few substances intentionally added to drinking water for health benefits, which raises important discussions about informed consent and public health policy.

Second, concerns about fluoride’s safety—especially at elevated levels in natural groundwater—persist in both rural areas that rely on unregulated private wells and urban regions served by public water systems. Third, as new research continues to emerge regarding fluoride’s sources and potential health effects, there is an ongoing need to reassess guidelines and educate the public.

In conclusion, I would like to emphasize that the decision to add fluoride to drinking water should be region-specific and science-based. As highlighted in a recent study, fluoride concentrations in groundwater vary significantly across the U.S. The study also found that, on a national scale, most groundwater has fluoride concentrations below 0.7 mg/L.

Therefore, in many parts of the country, the greater public health concern—if fluoridation is not implemented—may be an increased risk of tooth decay.