Fluoride Rule

Fluoride Rule


Fluoride can occur in drinking water naturally as a result of the geological composition of soils and bedrock. Some areas of the country have high levels of naturally occurring fluoride which can dissolve easily into ground water as it moves through gaps and pore spaces between rocks.

Fluoride can also be added to public drinking water supplies as a public health measure for reducing cavities among the treated population. Fluoridation is not required by EPA, which is prohibited by the Safe Drinking Water Act from requiring the addition of any substance to drinking water for preventive health care purposes. The Centers for Disease Control and Prevention (CDC) provides recommendations about the optimal levels of fluoride in drinking water in order to prevent tooth decay.

Health Effects

Public water systems with naturally occurring fluoride must treat their water supply to remove the excess fluoride to comply with the Safe Drinking Water Act limits. Children under nine years of age exposed to levels of fluoride greater than 2 mg/L may develop a condition known as mottling or discoloration of the permanent teeth. EPA set a non-enforceable secondary maximum contaminant level (SMCL) of 2 mg/L to protect against aesthetic or cosmetic effects. Federal regulations require that fluoride not exceed a concentration of 4 mg/L in drinking water and is the current enforceable maximum contaminant level (MCL). The MCL has been established to protect public health. Exposure to drinking water levels above 4 mg/L for many years may result in cases of crippling skeletal fluorosis, which is a serious bone disorder resembling osteopetrosis and characterized by extreme density and hardness and abnormal fragility of the bones (sometimes called “marble bones.”) EPA has recently completed a new risk and exposure assessment for orally ingested fluoride and have concluded that fluoride exposure among the population has increased in the last 40-50 years. From the data in this assessment, EPA has proposed a reference dose (RfD – estimate of the daily exposure likely to be without harmful effect during a lifetime) of 0.08 mg/kg/day for protection against pitting of tooth enamel and also to protect against fractures and skeletal effects in adults.

Maintaining Compliance

Fluoride levels in water are measured through a laboratory analyzed sample. Typical monitoring for Community Water Systems is one sample every three years. The frequency of sampling is dependent upon the concentration of fluoride in the water. Sample schedules can be increased to yearly, quarterly or daily. For systems adding fluoride, daily monitoring is required.

Public Notice

Community water systems that exceed the fluoride MCL of 4 mg/L must notify persons served by that system as soon as practical, but no later than 30 days after the system learns of the violation.

Community water systems that exceed the fluoride SCML of 2 mg/L must notify persons served by that system as soon as practical but no later than 12 months from the day the water system learns of the exceedance.



Diane Jordan
Chemical/Radiological/ Waiver Rule Manager
PO Box 200901
Helena, MT 59620
Phone: (406) 444-6741
Fax: (406) 444-1374
DEQ: (406) 444-4400