Fluoride
Also known as: F
Beneficial at low added levels for teeth, but a violation where natural groundwater concentrations run high.
MCL 4.0 mg/L (enforceable). EPA sets an enforceable 4.0 mg/L limit and a 2.0 mg/L secondary standard; systems that fluoridate target ~0.7 mg/L for dental health.
At the low levels added for dental health, fluoride reduces tooth decay. Well above the limit, long-term exposure can cause dental fluorosis and, at much higher chronic doses, skeletal fluorosis.
Naturally present in many groundwater sources; also intentionally added at low levels by many public systems for cavity prevention.
Reverse osmosis, activated alumina, and distillation remove fluoride where natural levels are high.
Source: EPA Safe Drinking Water Information System (SDWIS) · 2026 Q1
Fluoride is unusual: at about 0.7 mg/L it's deliberately added to protect teeth, but some groundwater naturally contains far more. EPA's enforceable 4.0 mg/L limit targets the high-natural-fluoride systems where overexposure, not deficiency, is the risk.
Most fluoride violations occur in groundwater systems sitting on fluoride-rich geology, where treatment is needed to bring naturally high levels down.
States with the most fluoride violations
Community water systems with a related health-based violation since 2016.
| # | State | Systems |
|---|---|---|
| 1 | Texas | 37 |
| 2 | California | 13 |
| 3 | New Mexico | 9 |
| 4 | Arizona | 8 |
| 5 | Georgia | 5 |
| 6 | Virginia | 5 |
| 7 | New Hampshire | 5 |
| 8 | Washington | 3 |
| 9 | Missouri | 3 |
| 10 | Alabama | 2 |
| 11 | Oklahoma | 1 |
| 12 | Montana | 1 |
Common questions
What is the EPA limit for fluoride in drinking water?
MCL 4.0 mg/L (enforceable). EPA sets an enforceable 4.0 mg/L limit and a 2.0 mg/L secondary standard; systems that fluoridate target ~0.7 mg/L for dental health.
Is fluoride in drinking water dangerous?
At the low levels added for dental health, fluoride reduces tooth decay. Well above the limit, long-term exposure can cause dental fluorosis and, at much higher chronic doses, skeletal fluorosis.
Where does fluoride in water come from?
Naturally present in many groundwater sources; also intentionally added at low levels by many public systems for cavity prevention.
How do I remove fluoride from my water?
Reverse osmosis, activated alumina, and distillation remove fluoride where natural levels are high.
Which states have the most fluoride violations?
Across U.S. community water systems, 102 have had a related health-based violation since 2016, led by Texas with 37.
Source: EPA — National Primary Drinking Water Regulations
Source: EPA — Fluoride