Why is There Fluoride in Water?

Table of Contents

Why is there fluoride in water? — and when did it start?

The story begins in Colorado in the early 1900s, when dentist Frederick McKay noticed that children drinking water from certain wells had mottled (but unusually decay-resistant) teeth. Epidemiologist H. Trendley Dean’s field surveys in the 1930s pinpointed fluoride as the common factor and calculated a “sweet-spot” concentration that prevented decay without unsightly staining. Guided by those data, Grand Rapids, Michigan, became the first city to adjust its water to 1 ppm fluoride on January 25 1945, kicking off a 15-year controlled trial that ultimately showed a >60 % drop in cavities among local schoolchildren.

By 1960 more than 3 million U.S. residents had fluoridated tap water; today about 209 million people—72 % of everyone on community water systems—receive it. The practice has been called one of the CDC’s “Ten Great Public-Health Achievements of the 20th Century.”

Benefits of Community Water Fluoridation

Benefit	Evidence	Reference
Fewer cavities	Communities with optimal fluoride average 25 % fewer caries across all ages. Early city-pair studies showed 50–70 % reductions in children; recent Cochrane reviews still find ~26 % relative reduction in permanent teeth.	CDC, NIDCR, Cochrane Review
Cost savings	Nationwide fluoridation prevents an estimated $6.5 billion in dental treatment costs annually—an ROI of roughly $20–38 per $1 invested.	CDC ROI Fact Sheet
Health equity	Universal dosing narrows decay gaps linked to income and dental-care access; the largest relative benefit is seen in low-income children.	CDC “Ten Great Public-Health Achievements” report

Potential side effects

Dental fluorosis is the main documented risk at U.S. levels. NHANES data show very-mild or mild fluorosis in ≈ 40 % of 12- to 15-year-olds, almost all of it cosmetic
Skeletal fluorosis appears only with decades of exposure to >4 mg/L. EPA therefore sets a Maximum Contaminant Level (MCL) of 4 mg/L—six times higher than the recommended level
Claims linking optimum-level fluoride to lower IQ or thyroid issues rely on studies of regions with naturally very high fluoride (>1.5 mg/L) and have not been replicated at 0.7 mg/L

Cavity rates since fluoridation

1945-1965: Early demonstration cities (Grand Rapids, New burgh, Evanston) logged 50–70 % fewer cavities after a decade.
1970s-1980s: National surveys saw the gap shrink to 18–40 % as fluoride toothpaste became common—but overall decay continued to fall.
2000-2020: CDC surveillance still attributes a 25 % caries reduction across the whole population to community water fluoride, with adults keeping natural teeth longer than any previous generation.

How does fluoride stop cavities?

Topical armor – Fluoride ions adsorb onto enamel during each sip or rinse, attracting calcium and phosphate and rebuilding early acid lesions as fluorapatite, which is ~4× more acid-resistant than normal enamel
Bacterial slowdown – In plaque fluid, fluoride lowers bacterial acid production by inhibiting enolase and other glycolytic enzymes.
Pre-eruptive benefit – While teeth are still developing, ingested fluoride becomes incorporated into enamel crystals, yielding slightly harder tooth surfaces.

How much fluoride should be in drinking water?

Since 2015 the U.S. Public Health Service has recommended a single national optimum of 0.7 mg per litre (ppm)—low enough to minimize fluorosis yet high enough to protect enamel. This replaced the 1962 climate-based range of 0.7–1.2 ppm.

For context, WHO advises 0.5–1.5 ppm depending on climate, and EPA’s enforceable health limit remains 4 ppm

Does every state fluoridate?

No—decisions are made by local utilities or, in a few cases, state law. Coverage (percentage of people on community water systems, 2022) ranges from Kentucky 99.7 % and DC 100 % to Hawaii 8.5 % and New Jersey 16.2 %. The national mean is 72.3%.

Water fluoridation in Washington and Idaho

State	% of CWS population with fluoridated water (2022)	Highlights
Washington	64.4 %	Seattle voters approved fluoridation in 1968; Seattle Public Utilities delivers 0.7 ppm to 1.5 million residents. Rural districts decide individually, so eastern counties have lower coverage.
Idaho	31.0 %	No statewide mandate; several midsize cities (e.g., Pocatello, Twin Falls) add fluoride, but most systems rely on natural levels that vary widely. Idaho’s 2022 Oral-Health Plan calls for expanding coverage.

Which countries don’t add fluoride to water?

Many high-income nations rely on alternative delivery (toothpaste, salt, or milk fluoridation) or already have adequate natural fluoride, so they do not practice community water fluoridation. These include: Germany, France, Italy, Sweden, Denmark, Norway, Finland, the Netherlands, Belgium, Austria, Switzerland, Iceland, and most regions of Spain and Japan. Several of these countries still endorse topical fluoride and show comparable modern cavity rates, underscoring that water fluoridation is one—but not the only—route to population oral-health gains.