But since the start of 2025, the U.S. government—aka new HHS secretary Robert F. Kennedy Jr.—has called for the removal of fluoride from water, calling it “a very bad way to deliver it to our systems,” and prompting the states of Utah and Florida to have it banned. 

Now a new study, published on Friday in the journal JAMA Health Forum, projects what the effects of removing fluoride from water nationwide would be—and the findings are a dentist’s nightmare: 25.4 million more cases of tooth decay (a 7.5% rise) at an approximate cost of $9.8 billion, all over five years. Researchers call it a best-case scenario.

“Our microsimulation estimated that removing fluoride from the public water system would result in greater numbers of dental caries [tooth decay], with associated higher costs to both quality of life and to the health care system,” wrote the study authors, Dr. Sung Eun Choi of the Harvard School of Dental Medicine’s Department of Oral Health Policy and Epidemiology, and Dr. Lisa Simon of Brigham and Women’s Hospital’s Division of General Internal Medicine. 

These effects, they wrote, “would disproportionately affect publicly insured and uninsured children, who are already at highest risk of unmet dental needs.” And although public-water fluoridation has potential benefits for all individuals, Choi and Simon added, “children with reduced access to dental care, such as those from families who are publicly insured, have low income, or live in rural areas, derive the most benefit, and our model found that removing fluoride would compound disparities in tooth decay.”

For the projection, the authors simulated a nationally representative sample of 10,000 US children to estimate changes in total costs, quality-adjusted life years (QALYs), and cumulative dental caries incidence with a removal of fluoride in the public water system accounting for differences in demographic composition, disease risks, and access to dental care across the populations residing in areas with different fluoride levels in public water systems.

Fluoride, the chemical ion of the mineral fluorine, is naturally present in trace amounts, according to the CDC, in soil, water, plants, and some food sources including shellfish, raisins, yogurt, and potatoes. It can also be a byproduct of aluminum, fertilizer, and iron ore manufacture, or released from volcanic emissions. 

Since 1962, the U.S. Public Health Service has recommended it be added to drinking water to prevent tooth decay, though it’s a decision made on a local, not federal, level, and is not enforceable. 

The idea of banning fluoride in water has been long fought for by activists largely on the fringes, but has exploded in the mainstream since RFK Jr.’s appointment by Donald Trump—with a controversial study, published in JAMA Pediatrics in January, fueling the fire with its finding of a clear relationship between high fluoride exposure and decreased I.Q. in children.

That meta-analysis prompted division among medical experts, with the journal publishing two opposing editorials alongside it—one of which said the findings “underscore the need to reassess the potential risks of fluoride during early brain development,” with the other cautioning against the study’s various methodological issues.

Now, concludes the new study, “This cost-effectiveness analysis found that cessation of public water fluoridation would increase tooth decay and health system costs in the US.”

And, continue the authors, “Despite concerns regarding toxic effects associated with high levels of fluoride, this model demonstrates the substantial ongoing benefits of water fluoridation at safe levels currently recommended by the US Environmental Protection Agency, the National Toxicity Program, and the Centers for Disease Control and Prevention.”

More on tap water:

• The new fluoride study dividing the public health world as RFK Jr. calls for a ban on adding it to water
• Utah becomes first state to ban fluoride in water after RKF Jr. says it has health risks. Here’s what science says
• The truth about American drinking water: Report shows widespread presence of hazardous chemicals