A brief history of America's love affair with fluoridated water — and why it's now up for debate

• RFK Jr. says under President Trump, he'll advise US water systems to remove fluoride.
• The federal government is not in charge of the US water supply. It's a local thing.
• Fluoride can prevent cavities and dental decay, especially in kids, but dosing is still controversial.

Robert F. Kennedy Jr., the man widely expected to become a health leader in President-elect Donald Trump's White House, has promised to lobby to remove fluoride from the American water supply.

Nearly 63% of the US population has fluoridated water flowing through their taps, according to the Centers for Disease Control and Prevention (CDC).

US health experts describe fluoridated water — a voluntary practice for local water districts — as one of modern medicine's greatest public health achievements, up there with the recognition that smoking is bad for you.

Meanwhile, Kennedy, a former environmental lawyer who was instrumental in the fight to clean up the Hudson River in New York, says there's no need to fluoridate drinking water anymore since most toothpaste contains fluoride.

He's not alone. An important debate over fluoride is gaining fresh steam among scientists and legal experts. Some recent studies suggest more research is still needed on safe fluoride levels for kids. Plus, a federal ruling in California this year questioned the US government's recommended dose.

While many medical professionals — chiefly dentists — support some level of fluoridation, there is growing agreement that we still aren't sure how much fluoride is too much.

120 years ago, fluoride was the mystery culprit behind brown teeth in Colorado

The reason most Americans have fluoride in their drinking water stretches back more than a century to a mysterious outbreak scattered across the Midwest and western US.

In the early 1900s, dentists started noticing that children in specific towns, including Colorado Springs, Colorado; Oakley, Idaho; and Bauxite, Arkansas, were developing hard, chocolate-colored teeth.

It took more than 20 years, but eventually, researchers discovered that these unusual brown stains were caused by high amounts of naturally occurring fluoride in the drinking water in certain areas of the country.

They also found that the fluoride — a mineral compound found in rocks and dirt — was strengthening teeth. It was hardening tooth enamel and helping to repair some early-stage tooth decay.

By 1945, scientists had learned enough about fluoride to harness the technique to prevent cavities for the masses. They proposed microdosing the mineral into the public water supply to give kids just enough fluoride to protect their teeth and help heal dental decay without giving them so much that their teeth would go brown.

The experiment worked.

In 1945, Grand Rapids, Michigan, was the first city to purposefully fluoridate its water. In the first 10 years of the program, the rate of cavities in kids decreased by more than 60%. Thus, the idea of fluoridated water as a boon for public health was born.

US water districts decide their own fluoride levels

Kennedy has said he'd aim to convince local authorities nationwide to remove any added fluoride from taps.

"I think fluoride is on its way out," Kennedy told NBC News the day after the election, adding: "I'm not going to compel anybody to take it out, but I'm going to advise the water districts. I'm going to give them good information about the science, and I think fluoride will disappear."

The federal government does not control water supplies in the US. That task is up to states and local water systems.

The US Environmental Protection Agency does mandate a limit for fluoride in tap water: four milligrams per liter. That limit is meant to prevent crippling health issues caused by excess fluoride intake, like a bone-weakening disease called skeletal fluorosis.

The US lowered fluoride levels in drinking water in 2015

The amount of fluoride added to a water supply varies not only by city and county but also by the individual water system supplying a given neighborhood.

For many years, the federal recommendation fluctuated based on location. In warmer climates — where it was assumed that kids consumed more water to stay cool — officials recommended 0.7 milligrams of fluoride per liter. Colder areas were advised to add 1.2 milligrams per liter.

After reviewing evidence in 2015, the US Public Health Service decided that the discrepancy wasn't needed. The recommendation for fluoridation is now set at 0.7 milligrams per liter nationwide.

Most major cities in the US hover around the 0.7 figure. Some places naturally have elevated levels of fluoride in their water due to geological factors. In Lordsburg, New Mexico, for example, water samples collected earlier this year had concentrations of fluoride between 5.2 and 6.4 milligrams per liter. Authorities there advise that children under 9 years old shouldn't drink tap water.

Places with fluoride-free water generally have worse dental health

Proponents of ditching fluoride often point to the many European countries that do not fluoridate their water. Those countries are not 100% fluoride-free, though: unlike people in the US, many Europeans consume fluoridated salt.

Hawaii is the only US state without any fluoride in municipal taps; fluoridated water is only available there on military bases. A 2015 report from Hawaii's health department said the state also has the highest prevalence of tooth decay among 3rd graders in the US.

"It's obvious; you can see it in the quality of their enamel," Anthony Kim, dental director at the Waimanalo Health Clinic, told the Honolulu Civil Beat in 2020. "Sadly, especially among the kids."

Researchers in Canada see the same phenomenon. The rate of cavities detected in Alberta spiked after the city went fluoride-free in 2011, according to a February 2024 study. Calgary did the same and saw similar tooth issues in kids. The city now plans to re-fluoridate its water supply, but cost issues and global supply chain problems post-pandemic have created delays.

The military supports fluoridation. In 2016, the US Department of Defense said dental decay was a "significant" reason military personnel were classified as non-deployable. As such, fluoridated water is now mandated on any military base with more than 3,300 people.

Rumors have circulated that drinking fluoridated water can lead to bone cancer (osteosarcoma), but long-term studies from both the UK and US haven't found any credible evidence of higher rates in areas where people drink fluoridated water.

Is there any truth to claims of IQ issues?

On November 2, Kennedy said on X that fluoride is an "industrial waste" that is linked to "IQ loss."

He linked to a ruling from a federal judge in California in October. The judge, appointed by former President Obama, said that while he could not "conclude with certainty" that fluoridated water could reduce the IQ of children, there is evidence that it can be "hazardous at dosages that are far too close to fluoride levels in the drinking water of the United States."

His ruling came weeks after a headline-grabbing paper in which a group of independent scientists reviewed existing evidence on fluoridation for the US National Toxicology Program. Their review concluded that some studies of fluoride consumption have found links between higher fluoride water levels and lower IQs in kids.

There are a couple of big caveats to keep in mind. First, those studies were conducted in other countries, including Canada, China, India, Iran, Pakistan, and Mexico, not the US.

Second, the association with lower IQs was only apparent when children were drinking water loaded with fluoride, at more than 1.5 milligrams per liter. That's double what's recommended in the US and 50% more fluoride than what was first used in Grand Rapids in 1945.

"More studies are needed to fully understand the potential for lower fluoride exposure to affect children's IQ," the experts said.

Those new studies are starting to trickle out. Fluoride and aluminum researcher Ashley Malin, an assistant professor of epidemiology at the University of Florida, recently found a potential link between a woman's fluoride levels during pregnancy and neurobehavioral problems in her toddler three years later.

"At this point, I would advise that pregnant women reduce their fluoride intake," Malin told Business Insider.

Malin brushes her teeth without fluoride, drinks filtered water (using a reverse osmosis water purifier or buying bottled water), and says that the most fluoride she consumes is probably from the black chai tea she occasionally drinks.

Settling on the right dose

It's hard to tease out exactly how beneficial fluoridated water is for preventing cavities, in part because fluoridating water isn't the only way that tooth care has improved dramatically since the 1940s. (The level of fluoride in many toothpastes is much higher than what's in the water.)

The California ruling last month didn't get prescriptive about what the EPA should do about all this uncertainty. It only recommended some kind of "regulatory action" on fluoride.

"It should be noted that this finding does not conclude with certainty that fluoridated water is injurious to public health," the verdict read.

A federal judge wants the EPA to better answer now whether 0.7 milligrams per liter of fluoride is safe enough.

The EPA has said in the past that reviewing their fluoride numbers is a "low priority" item for the agency. Public health experts and dentists generally agree that fluoridated tap water is a safe, effortless, and equitable way to ensure people get enough fluoride to prevent most childhood cavities.

However, scientists haven't quite settled on the optimal fluoride level in tap water to maintain healthy teeth yet.