Fluoride

What fluoride is and where it comes from

Fluoride is a natural form of the element fluorine, and it exists in nearly all water at some level. It dissolves out of rock and soil as groundwater moves through the ground, so almost every well and aquifer in the country carries at least a trace of it.

The amount varies widely by geology. The US Geological Survey has found naturally occurring fluoride levels that range from nearly zero to well above any recommended limit, with the highest concentrations in parts of the West and Southwest where the underlying rock is rich in fluoride-bearing minerals. In those areas, the fluoride in a glass of water comes from the ground, not a treatment plant. Elsewhere, utilities add it deliberately to reach a target level.

Why the US started fluoridating water

The story begins in Grand Rapids, Michigan. In 1945, it became the first city in the world to add fluoride to its public water supply, launching a study that tracked tooth decay in children over the following years.

The results were striking. Researchers found that decay rates among Grand Rapids children dropped by about 60%, the National Institute of Dental and Craniofacial Research reports. That finding drove rapid adoption across the country. The insight came from an earlier observation by dentist Frederick McKay, who noticed that people in areas with naturally high fluoride had fewer cavities, even as some showed stained teeth. Fluoridation set out to capture the cavity protection while keeping levels low enough to avoid the staining.

Fluoride works mainly by strengthening tooth enamel. It helps rebuild the mineral surface of a tooth after acid from bacteria and food wears it down, a process the CDC credits with reducing cavities across entire populations. The protection reaches everyone who drinks the water, regardless of income or access to a dentist, which is part of why public health agencies favor it.

The same mineral affinity that helps teeth also draws fluoride into bone. At normal levels this poses no problem, but the body stores fluoride in the skeleton over time, and very high, sustained exposure is where the concerns begin. The distinction between benefit and harm comes down almost entirely to dose.

Two federal numbers govern fluoride in drinking water, and they serve different purposes. The US Department of Health and Human Services sets the recommended level for fluoridation at 0.7 milligrams per liter, a target it lowered in 2015 from an older range of 0.7 to 1.2 to account for the fluoride people now get from toothpaste and other sources.

The EPA sets the enforceable safety limits. Its maximum contaminant level for fluoride is 4.0 milligrams per liter, the ceiling meant to protect against the most serious health effects. The EPA also sets a secondary, non-enforceable standard of 2.0 milligrams per liter aimed at limiting cosmetic effects on teeth. Utilities that add fluoride aim for the 0.7 target, while systems drawing water with high natural fluoride must treat it down if levels approach the 4.0 limit.

The debate over levels and overexposure

The main documented risk from too much fluoride is dental fluorosis. This is a cosmetic change to tooth enamel, ranging from faint white streaks to brown staining and pitting, that develops in childhood when teeth are still forming. The CDC reports that most fluorosis in the US is mild and appears as barely visible white spots, and it results from young children taking in fluoride from multiple sources at once, including swallowed toothpaste.

The more serious concern is skeletal fluorosis, a condition that stiffens and weakens bones after years of very high exposure. It is rare in the US, tied mostly to water with naturally high fluoride well above the recommended level. The EPA set its 4.0 milligram limit specifically to guard against this. The tension in the debate sits between the low, protective level utilities add and the high levels found naturally in some regions, which are the ones that carry real risk.

What recent research says

The fluoride conversation shifted in 2024. In August, the National Toxicology Program, part of HHS, released a review concluding with moderate confidence that fluoride exposure above 1.5 milligrams per liter is associated with lower IQ in children. The report drew heavily on studies from countries with naturally high fluoride, and it did not evaluate the 0.7 level used in US fluoridation.

The finding fueled ongoing scrutiny. Later in 2024, a federal judge ordered the EPA to review the risk fluoride may pose at current levels, though the ruling did not conclude that fluoridated water is unsafe. Public health groups, including the American Dental Association, continue to support fluoridation at the recommended level, pointing to decades of cavity reduction. The research points to a familiar theme: the concern rises with the dose, and the levels tied to harm sit above what US systems target.

What a household can do

Find out what is in your water first. If you are on a public system, your utility's annual Consumer Confidence Report lists the fluoride level, and the CDC's My Water's Fluoride tool shows whether your community adds it. Knowing your number tells you whether you have too little, an optimal amount, or a naturally high level worth addressing.

Private well owners carry more responsibility, since no agency tests or treats their water. The EPA and CDC recommend testing a well for fluoride through a state-certified laboratory, especially in regions known for high natural levels. If a test shows fluoride above the 4.0 limit, treatment matters. Reverse osmosis systems and activated alumina filters remove fluoride effectively, while standard carbon pitcher filters generally do not. For families with young children, watch the other sources: use a pea-sized amount of toothpaste, supervise brushing so children do not swallow it, and ask a pediatric dentist whether your child needs more or less fluoride based on your local water. Boiling does not remove fluoride and can slightly concentrate it, so it is not a fix.