Fluoride in Drinking Water

The federal primary MCL for fluoride is 4.0 mg/L — the enforceable health-based limit set by EPA. The CDC-recommended optimal fluoridation level is 0.7 mg/L, a Public Health Service recommendation that is separate from EPA's standard and reflects the concentration shown to reduce tooth decay without causing dental fluorosis. Your Consumer Confidence Report must disclose your system's measured fluoride level and, if required, include mandatory health-effects language from 40 CFR Part 141 Subpart O.

Where fluoride in drinking water comes from

Fluoride enters drinking water through two routes: natural occurrence and intentional addition.

Naturally occurring fluoride dissolves from fluoride-bearing minerals — primarily fluorite (calcium fluoride) and fluorapatite — into groundwater. Concentrations vary widely by geology. In some regions of the United States, particularly in parts of the Southwest, fluoride naturally exceeds 2.0 mg/L in groundwater. EPA lists "erosion of natural deposits" and "discharge from fertilizer and aluminum factories" as environmental sources. (EPA, National Primary Drinking Water Regulations table)

Community water fluoridation is the intentional adjustment of fluoride concentration in a public water supply to a level recommended to prevent tooth decay. EPA classifies fluoride as a "water additive which promotes strong teeth" in its regulated contaminants table. (EPA, National Primary Drinking Water Regulations) Fluoridation has been practiced in the United States since 1945; the practice is administered by water utilities, not by EPA, and the recommended concentration is set by the U.S. Public Health Service, not by the MCL framework.

Health effects

Required CCR health-effects disclosure (Appendix A to Subpart O of Part 141)

Federal regulations require every community water system to include health-effects information in the CCR for each detected regulated contaminant. For fluoride, Appendix A to Subpart O of Part 141 (40 CFR Part 141) specifies the following potential health effects from long-term exposure above the MCL:

"Bone disease (pain and tenderness of the bones); Children may get mottled teeth."

(40 CFR Part 141, Subpart O, Appendix A — Regulated Contaminants; EPA National Primary Drinking Water Regulations)

Systems detecting fluoride at any level must include this language and the associated MCL and MCLG values in the regulated contaminants table. The table must appear in every CCR regardless of whether the result is above or below the MCL. (40 CFR § 141.153(b); 40 CFR § 141.153(f))

What the science says about each effect

Dental fluorosis. Fluoride consumed during tooth development (roughly birth through age 8) can affect enamel formation. At low to moderate concentrations — typically 0.7 to 2.0 mg/L — the effect is primarily cosmetic: white spots or streaking on tooth enamel. At concentrations above the secondary MCL of 2.0 mg/L, more pronounced pitting or brown staining may occur. ATSDR describes dental fluorosis as "a cosmetic condition that affects the appearance of tooth enamel" and identifies it as the most common effect of elevated fluoride exposure in the United States. (ATSDR, ToxFAQs for Fluoride)

Skeletal fluorosis. Chronic exposure to fluoride at elevated concentrations over many years can increase bone density while decreasing bone quality, leading to joint stiffness, pain, and reduced mobility. ATSDR identifies skeletal fluorosis as the primary concern at sustained high exposures. (ATSDR, ToxFAQs for Fluoride) The primary MCL of 4.0 mg/L is set to protect against skeletal fluorosis.

Current EPA review. On January 22, 2026, EPA released a Fluoride Human Health Toxicity Assessment: Preliminary Assessment Plan and Literature Survey for public comment (Federal Register docket EPA-HQ-OW-2025-3823), accelerating a review that was not otherwise due until 2030. EPA committed on April 7, 2025 to "expeditiously review new scientific information on potential health risks of fluoride in drinking water." The MCL of 4.0 mg/L remains in effect while this reassessment proceeds. (EPA, Fluoride in Drinking Water)

The two federal levels: primary MCL (4.0 mg/L) and secondary MCL (2.0 mg/L)

Primary MCL — 4.0 mg/L

The primary MCL for fluoride is 4.0 milligrams per liter (mg/L), set under the Safe Drinking Water Act (SDWA) and codified at 40 CFR § 141.62. It is enforceable: systems that exceed it are in violation and must notify customers and take corrective action. The MCLG is also set at 4.0 mg/L, matching the primary MCL — meaning EPA concluded there is a level of fluoride that is both protective and achievable. (40 CFR § 141.62; 40 CFR § 141.51)

EPA last formally set the primary fluoride MCL in 1985–1986 (50 FR 47142; 51 FR 11396). The MCL was reviewed again in 2024 as part of EPA's Six-Year Review process — the periodic evaluation EPA uses to determine whether existing MCLs need revision based on updated science. That review did not change the 4.0 mg/L level. EPA's 2026 accelerated toxicity reassessment (EPA-HQ-OW-2025-3823) may inform a future revision. (EPA, Fluoride in Drinking Water)

The statutory authority is SDWA § 1412 (42 U.S.C. § 300g-1), which directs EPA to set MCLs as close to the MCLG as is feasible. (42 U.S.C. § 300g-1)

Secondary MCL — 2.0 mg/L

The secondary MCL for fluoride is 2.0 mg/L, codified at 40 CFR § 143.3 under 40 CFR Part 143. It is not enforceable — EPA characterizes secondary standards as guidance for cosmetic effects rather than health-based limits. The secondary MCL for fluoride addresses tooth discoloration and pitting (dental fluorosis) caused by excess fluoride during childhood tooth development. EPA describes it as "a guideline for an upper boundary level in areas which have high levels of naturally occurring fluoride." (EPA, Secondary Drinking Water Standards — Guidance for Nuisance Chemicals; 40 CFR § 143.3)

When a system's fluoride level exceeds the secondary MCL of 2.0 mg/L, EPA requires public notification. (40 CFR § 141.208) The notification informs customers of the cosmetic risk but does not constitute a health violation.

The gap between the secondary MCL (2.0 mg/L) and the primary MCL (4.0 mg/L) is intentional. The range between them represents concentrations that EPA considers cosmetically concerning but not acutely health-threatening under the current standard.

The CDC-recommended optimal fluoridation level (0.7 mg/L)

The CDC-recommended optimal fluoridation level is 0.7 mg/L. This is a recommendation of the U.S. Public Health Service (USPHS), not an EPA drinking water standard. It does not appear in 40 CFR Part 141 and is not an MCL, MCLG, or any enforceable regulatory limit.

The recommendation was updated to 0.7 mg/L in 2015 by the U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation. The prior range had been 0.7 to 1.2 mg/L, set in 1962; the 2015 revision lowered the upper end to a single number reflecting updated evidence on fluoride's dental benefits and the increased availability of fluoride from other sources (fluoride toothpaste, dental treatments). The recommendation is documented in: U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries. Public Health Rep. 2015;130(4):318–331. (CDC, Community Water Fluoridation)

CDC recognizes community water fluoridation as one of the ten great public health achievements of the 20th century. The agency states: "The recommended fluoride concentration in drinking water (also called the optimal level) is 0.7 milligrams of fluoride per liter of water." (CDC, Community Water Fluoridation)

Water systems that fluoridate their water to the 0.7 mg/L level are operating well below both the primary MCL (4.0 mg/L) and the secondary MCL (2.0 mg/L).

Why these three numbers exist

The three fluoride levels serve three distinct regulatory and public health purposes:

| Level | Value | Who sets it | Purpose | Enforceable? | |---|---|---|---|---| | Primary MCL | 4.0 mg/L | EPA (40 CFR § 141.62) | Prevent skeletal fluorosis and bone disease; health-based limit | Yes — violations trigger mandatory action | | Secondary MCL | 2.0 mg/L | EPA (40 CFR § 143.3) | Prevent significant dental fluorosis (cosmetic); guidance for naturally fluoridated areas | No — public notice required, not a violation | | Optimal fluoridation level | 0.7 mg/L | USPHS / CDC (2015) | Maximize caries prevention while minimizing dental fluorosis; target for intentional fluoridation programs | No — a public health recommendation, not a regulation |

The primary MCL answers: at what concentration does fluoride cause a health risk that federal law requires water systems to prevent? The answer is 4.0 mg/L.

The secondary MCL answers: at what concentration does fluoride cause cosmetic effects significant enough to require public notice? The answer is 2.0 mg/L.

The optimal fluoridation level answers: what concentration delivers the greatest dental health benefit with the least risk of cosmetic fluorosis? The answer is 0.7 mg/L.

A system that adds fluoride to reach 0.7 mg/L, detects 0.7 mg/L in its annual monitoring, and reports that level in its CCR is in full compliance with all three frameworks.

How fluoride is monitored

Community water systems must monitor fluoride concentrations under 40 CFR Part 141. The monitoring frequency depends on system size, source water type, and whether the system adds fluoride. Systems that add fluoride must monitor more frequently to confirm the level stays at or near the 0.7 mg/L target; systems with naturally occurring fluoride from groundwater must also monitor regularly because concentrations can vary.

EPA's Six-Year Review process periodically re-evaluates fluoride MCLs alongside all other regulated contaminants. The review initiated in 2024, combined with the accelerated toxicity assessment announced in January 2026, means fluoride monitoring requirements may be revised if EPA concludes the science supports a lower MCL. Any revision would go through the full SDWA rulemaking process — proposed rule, public comment, and final rule. (EPA, Fluoride in Drinking Water)

The statutory framework for fluoride monitoring is SDWA § 1412 (42 U.S.C. § 300g-1) for the primary MCL, and SDWA § 1401(1)(B) (42 U.S.C. § 300f) for secondary standards. The CCR disclosure obligations derive from SDWA § 1414(c)(4) (42 U.S.C. § 300g-3(c)(4)), as amended by the 1996 SDWA amendments (Pub. L. 104-182) and the America's Water Infrastructure Act of 2018 (AWIA, Pub. L. 115-270). (42 U.S.C. § 300g-3(c)(4))

What utilities must disclose on the CCR

Every community water system that detects fluoride — at any level — must include fluoride in the regulated contaminants table of its annual CCR. The table must show:

(40 CFR § 141.153(b); Appendix A to Subpart O of Part 141)

If a system adds fluoride, the CCR should also note that fluoride is a water additive. Systems that fluoridate may choose — though are not required by federal rule — to include a statement about the optimal level or the purpose of fluoridation.

If fluoride exceeds the primary MCL of 4.0 mg/L, the system is in violation and must additionally include the required violation language under 40 CFR § 141.153(d). If fluoride exceeds the secondary MCL of 2.0 mg/L but not the primary MCL, the system must issue public notification per 40 CFR § 141.208 but is not in primary MCL violation.

California water systems have additional context at /ccr/state/california/, where state-specific secondary standards and the California Department of Drinking Water's guidance on fluoride reporting are covered.

For definitions of the terms used in the regulated contaminants table, see MCL and MCLG. For a full list of regulated contaminants and their CCR disclosure requirements, see Regulated contaminants in your CCR.

Sources cited

Last reviewed: 2026-05-03. Next scheduled review: every 6 months or after EPA Six-Year Review updates.