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Fluoride in Well Water: Natural vs. Added, and What to Test For

Private wells don’t get fluoride added to them. But naturally occurring fluoride exists in groundwater in certain parts of the country, and levels above the EPA limit are a real concern in those regions. This page is about natural fluoride in well water, which is a geology issue, not a fluoridation debate.

The two topics are easy to confuse because they share the same contaminant name. They’re different problems with different causes and different solutions.

How Natural Fluoride Gets Into Well Water

Fluoride occurs naturally in soil and rock. When groundwater moves through fluoride-bearing minerals, it picks up dissolved fluoride. The main sources are fluorite (calcium fluoride), fluorspar, and fluorapatite deposits in bedrock. Volcanic rock, certain granites, and some sedimentary formations contain these minerals in higher concentrations.

The geography matters. Parts of Arizona, Nevada, New Mexico, and the Texas border region sit above aquifers with naturally elevated fluoride. In these areas, well water fluoride above the EPA MCL of 4.0 mg/L isn’t unusual. Parts of southern Appalachia, including areas of Tennessee, Virginia, and West Virginia, also have localized fluoride hotspots tied to specific bedrock formations.

Depth matters too. Shallower wells tend to interact with different geology than deep wells. In some areas, deeper wells actually hit higher-fluoride aquifer zones. There’s no reliable rule about depth, which is why testing is the only answer.

The Three Fluoride Numbers and What Each One Means

Three different fluoride thresholds appear in discussions about drinking water. They serve different purposes and shouldn’t be compared to each other directly.

EPA MCL: 4.0 mg/L. This is the enforceable legal limit for public water systems. It’s set to prevent skeletal fluorosis, a condition involving bone and joint damage that results from long-term high fluoride intake. At this threshold, the primary concern is bone health in adults drinking high-fluoride water for years or decades.

EPA Secondary MCL: 2.0 mg/L. This is a non-enforceable aesthetic guideline. It’s set to prevent dental fluorosis, which causes discoloration and pitting of tooth enamel. It primarily affects children during tooth development. Levels between 2.0 and 4.0 mg/L sit in a zone where dental fluorosis is a concern but skeletal fluorosis hasn’t been established as a risk.

HHS Recommendation: 0.7 mg/L. This is the U.S. Department of Health and Human Services’ recommended level for fluoridation of public water systems. It’s set at a level thought to provide dental health benefits in children while staying well below the aesthetic and health thresholds. This number applies to fluoridation decisions. It’s not a contaminant threshold.

A well testing at 3.0 mg/L is above the aesthetic secondary standard but below the health MCL. A well at 5.0 mg/L exceeds the health MCL and warrants treatment. A well at 0.3 mg/L is doing nothing different than most public water systems. Those are three completely different situations.

Health Effects at High Natural Fluoride Levels

The health concern from high natural fluoride is at the upper end of the scale, not the low end.

Skeletal fluorosis requires long-term exposure above the EPA MCL of 4.0 mg/L. It affects joints and bones, causing pain and stiffness in mild cases and severe bone deformity in extreme cases. The 4.0 mg/L MCL is specifically designed to protect against this.

Dental fluorosis occurs during tooth development in children. It can appear at levels above 2.0 mg/L, though the severity increases at higher concentrations. Mild dental fluorosis causes white spots or streaks on teeth. Severe dental fluorosis causes brown staining and pitting.

If your well is in a higher-risk region and you have children, testing for fluoride is more pressing than it would be for an adult-only household, because the secondary standard exists specifically to protect developing teeth.

Testing Your Well for Fluoride

A state-certified water testing lab is the right call. Fluoride is included in most broad well water panels, though you can also order it as a standalone test if you’ve tested everything else recently.

In most of the country, a single test is enough to understand your baseline. If your result is below 1.0 mg/L, fluoride isn’t a significant concern for your well. If it’s between 1.0 and 2.0 mg/L, you’re in the range where periodic monitoring makes sense. Above 2.0 mg/L, treatment is worth considering, especially with children in the home. Above 4.0 mg/L, treatment is the right move.

You can find state-certified labs through your state health department or the EPA’s Safe Drinking Water Hotline. The best mail-in water tests page covers lab options that test for fluoride.

What Removes Fluoride From Well Water

Most standard filters don’t remove fluoride effectively. Activated carbon, the media in most pitcher filters and faucet filters, doesn’t work for fluoride at typical well water concentrations. Water softeners don’t remove fluoride. These are common misconceptions.

What does work:

Reverse osmosis (RO) is the most practical option for most households. An RO system certified to NSF/ANSI 58 has been tested and verified for fluoride reduction. Under-sink RO handles drinking and cooking water. A full whole-house RO is expensive and usually not needed for fluoride alone.

Activated alumina is a filter media specifically effective for fluoride and arsenic. It’s used in some dedicated fluoride-removal filters and point-of-use systems. Look for NSF/ANSI 58 certification if fluoride reduction is the goal.

Bone char is a traditional filter media derived from animal bones that adsorbs fluoride. It’s effective but less commonly available in standard residential products. It’s used in some specialty filters.

For the full treatment guide, see how to remove fluoride from water.

Related pages: Fluoride in Drinking Water | Well Water Testing Guide | Best Mail-In Water Tests

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Frequently Asked Questions

Is there fluoride in private well water?
Private wells are not fluoridated. But naturally occurring fluoride exists in some groundwater because of the geology. Parts of Arizona, Nevada, New Mexico, Texas, and southern Appalachia have bedrock or aquifer sediments with elevated natural fluoride. Wells in these areas can have fluoride above the EPA MCL of 4.0 mg/L without any human activity. This is a separate issue from the public debate about water fluoridation.
What is the EPA limit for fluoride in drinking water?
The EPA has two fluoride standards. The enforceable MCL is 4.0 mg/L, set to prevent skeletal fluorosis (bone damage from long-term high exposure). There's also a non-enforceable Secondary MCL of 2.0 mg/L, meant to prevent dental fluorosis (discoloration and pitting of tooth enamel). The HHS recommendation for fluoridation of public water is 0.7 mg/L, which is a much lower level set for dental health benefits in children.
Should I test my well for fluoride?
If you're in Arizona, Nevada, New Mexico, southern Texas, or parts of Appalachia (Tennessee, Virginia, West Virginia), testing makes sense, especially if you haven't tested your well recently. For most other regions of the country, natural fluoride in well water isn't a significant concern. A standard well water panel from a certified lab typically includes fluoride.
Does a Brita filter remove fluoride?
Standard Brita filters don't remove fluoride. Brita's filter media (activated carbon) isn't effective against fluoride at typical well water concentrations. To remove fluoride, you need reverse osmosis (NSF/ANSI 58 certified), activated alumina, or bone char filters. Always verify the specific product's NSF certification for fluoride reduction before buying.
Does my well water have fluoride added to it?
No. Fluoride is added only to community public water systems, and only in communities where the local government has chosen to fluoridate. Private wells are not connected to any fluoridation program. Any fluoride in your well water is naturally occurring from geology.