Most tap water in the United States contains about 0.7 milligrams per liter (mg/L) of fluoride, which is the level recommended by the U.S. Public Health Service for preventing tooth decay while minimizing side effects. That said, the actual amount in your tap depends on whether your community adds fluoride, how much occurs naturally in your local groundwater, and what kind of filtration your water goes through before it reaches you.
The Recommended Level: 0.7 mg/L
In 2015, the U.S. Public Health Service set 0.7 mg/L as the single recommended concentration for community water fluoridation. Before that, the range was 0.7 to 1.2 mg/L, adjusted by climate (the thinking was that people in hotter areas drink more water). The updated recommendation settled on the lower end after considering that Americans now get fluoride from multiple sources: toothpaste, mouthwash, and processed foods and beverages made with fluoridated water. The goal was to keep enough fluoride in the water to protect teeth while reducing the risk of dental fluorosis, a cosmetic change to tooth enamel caused by too much fluoride during childhood.
About 73% of the U.S. population served by community water systems receives fluoridated water. If your community participates, the target is that 0.7 mg/L number. The EPA, meanwhile, sets a legal ceiling: the maximum contaminant level for fluoride is 4.0 mg/L, a safety standard originally established in 1986 and most recently reviewed in 2024.
Natural Fluoride Levels in Groundwater
Fluoride isn’t only added to water. It’s a mineral that occurs naturally in rock and soil, and it dissolves into groundwater at varying concentrations depending on local geology. A study of over 38,000 wells across the U.S. found that the median fluoride concentration in untreated groundwater is around 0.2 mg/L. Most wells fall well below the recommended level: about 87% of domestic wells tested had fluoride concentrations under 0.7 mg/L.
In some regions, though, natural levels run high. Around 2.6% of domestic wells exceeded 2 mg/L, and 0.6% topped the EPA’s 4 mg/L safety limit. The highest concentration recorded in the study was 160 mg/L, from a monitoring well in California’s Basin and Range aquifers. If you rely on a private well, your water isn’t regulated by community fluoridation programs, and there’s no guarantee of what you’re getting without testing it.
How to Check Your Local Fluoride Level
The CDC offers a tool called “My Water’s Fluoride” that lets you look up fluoride data for participating community water systems by state. It’s useful as a starting point, but it has limitations: not all states participate, the data isn’t updated in real time, and reporting is voluntary. Your most reliable source is your local water utility, which is required to publish an annual water quality report (sometimes called a Consumer Confidence Report). This document lists fluoride levels along with other water quality metrics and is typically available on the utility’s website or by request.
If you use a private well, you’ll need to have your water tested independently. State health departments and cooperative extension offices can point you toward certified labs.
How Fluoride Protects Teeth
Fluoride works primarily at the tooth surface. When bacteria in your mouth feed on sugars, they produce acids that pull minerals out of enamel, a process called demineralization. Fluoride reverses this by helping calcium and phosphate redeposit into weakened enamel, forming a compound that’s harder and more acid-resistant than the original tooth surface. It also slows the growth of plaque bacteria, reducing acid production in the first place.
Drinking fluoridated water provides a steady, low-level topical exposure. Every time you take a sip, fluoride bathes your teeth. Some of it also enters your bloodstream and shows up in saliva, extending the protective effect between drinks. For children whose permanent teeth are still forming below the gumline, ingested fluoride gets incorporated into the developing enamel structure, building in resistance before the teeth even emerge.
Early studies in the mid-20th century found that community water fluoridation reduced cavities in children by 50% to 70%. As fluoride toothpaste became widespread and overall cavity rates dropped, the measurable benefit of fluoridated water narrowed. By the 1980s, children in fluoridated communities had about 18% fewer cavities than those in non-fluoridated areas. A review of U.S. studies from 1979 to 1989 found reductions of 8% to 37% among adolescents, with an average around 27%. In adults, fluoridation reduces cavities by 20% to 40%.
Dental Fluorosis: The Main Risk
The primary concern with fluoride in drinking water is dental fluorosis, which happens when children ingest too much fluoride during the first eight years of life, while their permanent teeth are developing. It’s a cosmetic issue, not a disease. In its mildest forms, it appears as faint white streaks or flecks on the teeth that are barely noticeable. Moderate cases show more widespread white opaque patches covering over half the tooth surface. Severe fluorosis, which is rare, involves pitting and brown staining.
The vast majority of fluorosis cases in the U.S. are very mild or mild. The prevalence of fluorosis has increased over the decades as fluoride sources have multiplied. Young children swallowing fluoride toothpaste is a significant contributor, which is why the standard advice is to use only a rice-grain-sized smear of fluoride toothpaste for children under three, and a pea-sized amount for ages three to six. The 2015 decision to lower the recommended water fluoride level from a range down to 0.7 mg/L was made in part to address this trend.
Removing Fluoride From Your Water
Standard pitcher filters and refrigerator filters that use activated carbon don’t remove fluoride. If you want to reduce fluoride levels at home, you need a more specialized system.
- Reverse osmosis (RO) is the most common household option. Studies show RO systems remove roughly 50% to 85% of fluoride, depending on the unit and whether it includes a total dissolved solids controller. Systems with a TDS controller tend to remove more.
- Distillation effectively removes fluoride by boiling water and collecting the steam, leaving minerals behind.
- Activated alumina filters are specifically designed for fluoride and arsenic removal, often used in point-of-use systems.
Keep in mind that boiling water does not remove fluoride. It actually concentrates it slightly as some water evaporates. If you’re on a fluoridated municipal supply and want to reduce your intake, an under-sink RO system is the most practical route for most households.