Side Effects of Fluoride in Water: What Each Authority Says
Official sources tie different effects to different fluoride levels. EPA's 2.0 mg/L secondary standard guards against tooth discoloration and pitting; NTP concluded, with moderate confidence, that water above 1.5 mg/L is associated with lower IQ in children; and EPA lists bone disease as the potential health effect of long-term exposure above its enforceable 4.0 mg/L limit.
Key numbers
0.7 mg/L
U.S. Public Health Service recommendation
The U.S. Public Health Service recommends 0.7 mg/L for community water systems that add fluoride.
Verified
1.5 mg/L
WHO guideline value
The World Health Organization's guideline value for fluoride in drinking water is 1.5 mg/L.
Verified
1.5 mg/L
National Toxicology Program (2024)
NTP's 2024 monograph concluded, with moderate confidence, that drinking water containing more than 1.5 mg/L is associated with lower IQ in children.
Verified
2.0 mg/L
EPA secondary standard (non-enforceable)
EPA's secondary (non-enforceable) standard for fluoride is 2.0 mg/L, and exceeding it requires a special public notice.
Verified
4.0 mg/L
EPA maximum contaminant level (enforceable)
EPA's enforceable maximum contaminant level (MCL) for fluoride is 4.0 mg/L, and its health goal (MCLG) is also 4.0 mg/L.
Verified
Where does your water fall?
Our ZIP check shows the fluoride level each water system serving a ZIP code reported, where our data has one, and where that level sits against the levels in the table above.
Dental fluorosis
EPA's secondary standard for fluoride is 2.0 mg/L. It is not enforceable and is set to guard against tooth discoloration and pitting; a system that exceeds it must issue a special public notice. CDC states that when fluoride in a water system exceeds 2.0 mg/L, the system must notify its customers of the increased potential for dental fluorosis.
The U.S. Public Health Service's 0.7 mg/L recommendation is meant to keep fluoride's tooth-decay prevention benefit while reducing the risk of dental fluorosis.
CDC says formula mixed with fluoridated water may increase the chance of dental fluorosis if it is a child's main source of food; ready-to-feed formula contains little fluoride.
Sources: U.S. Environmental Protection Agency (Verified ); Centers for Disease Control and Prevention (Verified ); U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation (Public Health Reports 2015;130(4):318–331) (Verified )
IQ and neurodevelopment
In its 2024 monograph, the National Toxicology Program concluded, with moderate confidence, that drinking water containing more than 1.5 mg/L fluoride is associated with lower IQ in children.
The same review found insufficient data to determine whether 0.7 mg/L, the level recommended for U.S. community water, has a negative effect on children's IQ.
Source: National Toxicology Program (NIEHS) (Verified )
Skeletal fluorosis and bone
EPA's National Primary Drinking Water Regulations list bone disease (pain and tenderness of the bones) as the potential health effect of long-term exposure to fluoride above the 4.0 mg/L maximum contaminant level, and note that children may get mottled teeth.
The U.S. Public Health Service's 2015 recommendation reports that the 2006 National Research Council review concluded that stage III skeletal fluorosis, a clinical stage associated with significant bone or joint damage, appears to be a rare condition in the United States, and that the committee could not determine whether stage II skeletal fluorosis is occurring in U.S. residents who drink water with fluoride at 4 mg/L.
Sources: U.S. Environmental Protection Agency (Verified ); U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation (Public Health Reports 2015;130(4):318–331) (Verified )
Thyroid
The U.S. Public Health Service's 2015 recommendation reports that the 2006 National Research Council review considered a potential association between fluoride exposure at the concentrations it examined and changes in the thyroid, parathyroid, and pineal glands in experimental animals and humans.
The report noted that available studies of the effects of fluoride exposure on endocrine function have limitations. The review called for better measurement of fluoride exposure in epidemiological studies and for further research on the mechanisms of fluoride's action on the endocrine system.
Source: U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation (Public Health Reports 2015;130(4):318–331) (Verified )
Bone cancer (osteosarcoma)
The U.S. Public Health Service's 2015 recommendation describes a later study of osteosarcoma, a type of bone cancer, that assessed fluoride exposure using actual bone fluoride concentration; it showed no significant association between bone fluoride levels and osteosarcoma risk.
Source: U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation (Public Health Reports 2015;130(4):318–331) (Verified )
Recent events in research, the courts, regulation and state law
The events below are recent and dated, each with its source: a federal monograph, a court order and its vacatur, a federal review and three state laws.
NTP monograph: moderate confidence that fluoride above 1.5 mg/L is associated with lower IQ in children. (National Toxicology Program (NIEHS))
A federal district court (N.D. Cal.) finds that fluoridation at the level considered optimal in the U.S. poses an unreasonable risk of reduced IQ in children under TSCA, and requires an EPA regulatory response. (U.S. District Court, N.D. Cal. (Case 3:17-cv-02162-EMC, Doc. 445))
Vacated : The Ninth Circuit vacates the 2024 district court fluoride decision and remands. (U.S. Court of Appeals for the Ninth Circuit (No. 25-384; filed as N.D. Cal. Doc. 508))
EPA commits to an expedited review of fluoride in drinking water. (U.S. Environmental Protection Agency)
Utah's H.B. 81 took effect on May 7, 2025. (Utah State Legislature)
Utah's H.B. 81 (2025) provides that a person may not add fluoride to water in, or water that will be introduced into, a public water system, and that a political subdivision may not enact or enforce an ordinance that requires or permits it. (Utah State Legislature)
Florida SB 700, approved by the governor on May 15, 2025 as Chapter 2025-22, took effect on July 1, 2025. (The Florida Senate)
The National Conference of State Legislatures, in a snapshot updated September 24, 2025, names Utah and Florida as the first states to enact laws prohibiting the addition of fluoride in public water systems, Florida's SB 700 by prohibiting additives that do not meet its definition of water quality additives. (National Conference of State Legislatures)
Louisiana's Act 731, effective June 2, 2026, lets any water system opt out of the state fluoridation requirement through a voter petition and a local election; the requirement otherwise remains. (Louisiana State Legislature)
What is settled and what is still open
Set in regulation: EPA set the enforceable 4.0 mg/L limit in 1986, as a standard designed to prevent known or anticipated adverse health effects, and most recently reviewed it in 2024.
Under review: EPA committed on April 7, 2025 to an expedited review of fluoride under the Safe Drinking Water Act, released a Preliminary Assessment Plan and Literature Survey on January 22, 2026, and released a Protocol for Developing the Fluoride Human Health Toxicity Assessment on August 3, 2026. As of 2026-10-11, EPA's Fluoride in Drinking Water page does not mention a proposal or proposed rule to change the fluoride MCL.
Not yet determined: NTP found insufficient data to determine whether 0.7 mg/L has a negative effect on children's IQ.
In court: On May 21, 2026 the Ninth Circuit vacated the district court's 2024 fluoride decision and remanded the case.
Sources: U.S. Environmental Protection Agency (Verified ); National Toxicology Program (NIEHS) (Verified ); U.S. Court of Appeals for the Ninth Circuit (No. 25-384; filed as N.D. Cal. Doc. 508) (Verified )
More on fluoride
Frequently asked questions
What are the downsides of fluoride in drinking water?
The effects official sources tie to fluoride depend on the level. CDC states that when fluoride in a water system exceeds 2.0 mg/L, the system must notify its customers of the increased potential for dental fluorosis. In its 2024 monograph, the National Toxicology Program concluded, with moderate confidence, that drinking water containing more than 1.5 mg/L fluoride is associated with lower IQ in children. The same review found insufficient data to determine whether 0.7 mg/L, the level recommended for U.S. community water, has a negative effect on children's IQ. EPA's National Primary Drinking Water Regulations list bone disease (pain and tenderness of the bones) as the potential health effect of long-term exposure to fluoride above the 4.0 mg/L maximum contaminant level, and note that children may get mottled teeth.
Sources
- U.S. Environmental Protection Agency. “Secondary Drinking Water Standards: Guidance for Nuisance Chemicals”. https://www.epa.gov/sdwa/secondary-drinking-water-standards-guidance-nuisance-chemicals (Verified )
- National Toxicology Program (NIEHS). “Fluoride Exposure: Neurodevelopment and Cognition”. https://ntp.niehs.nih.gov/whatwestudy/assessments/noncancer/completed/fluoride (Verified )
- U.S. Environmental Protection Agency. “National Primary Drinking Water Regulations”. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations (Verified )
- U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation (Public Health Reports 2015;130(4):318–331). “U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries”. https://pmc.ncbi.nlm.nih.gov/articles/PMC4547570/ (Verified )
- World Health Organization. “Guidelines for drinking-water quality: fourth edition incorporating the first and second addenda (2022)”. https://iris.who.int/handle/10665/352532 (Verified )
- Centers for Disease Control and Prevention. “Frequently Asked Questions about Community Water Fluoridation”. https://www.cdc.gov/fluoridation/faq/index.html (Verified )
- U.S. District Court, N.D. Cal. (Case 3:17-cv-02162-EMC, Doc. 445). “Findings of Fact and Conclusions of Law (Sept. 24, 2024)”. https://storage.courtlistener.com/recap/gov.uscourts.cand.310380/gov.uscourts.cand.310380.445.0.pdf (Verified )
- U.S. Court of Appeals for the Ninth Circuit (No. 25-384; filed as N.D. Cal. Doc. 508). “Memorandum, Food & Water Watch v. EPA, No. 25-384 (9th Cir. May 21, 2026)”. https://storage.courtlistener.com/recap/gov.uscourts.cand.310380/gov.uscourts.cand.310380.508.0.pdf (Verified )
- U.S. Environmental Protection Agency. “Fluoride in Drinking Water”. https://www.epa.gov/sdwa/fluoride-drinking-water (Verified )
- Utah State Legislature. “H.B. 81 Fluoride Amendments (Enrolled Copy)”. https://le.utah.gov/Session/2025/bills/enrolled/HB0081.pdf (Verified )
- The Florida Senate. “CS/CS/CS/SB 700 (2025) bill history”. https://www.flsenate.gov/Session/Bill/2025/700 (Verified )
- National Conference of State Legislatures. “State of the Tap: Policy Actions on Fluoride in Drinking Water”. https://www.ncsl.org/health/state-of-the-tap-policy-actions-on-fluoride-in-drinking-water (Verified )
- Louisiana State Legislature. “Résumé Digest, Act 731 (SB 4), 2026 Regular Session”. https://www.legis.la.gov/legis/ViewDocument.aspx?d=1483254 (Verified )
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"Side Effects of Fluoride in Water: What Each Authority Says". TapWaterData, last reviewed 2026-10-11. https://www.tapwaterdata.com/fluoride/health-effects