Well Water Nerd

Fluoride in well water

1in5

private wells tested in Lincoln County, Missouri had fluoride above the limit, the highest share of any county, according to Missouri DHSS private well sampling summaries.

Natural fluoride in bedrock wells can exceed the limit. Above 4 mg/L long-term exposure causes skeletal fluorosis; above 2 mg/L children can develop tooth mottling.

EPA limit
4 mg/L (EPA MCL (40 CFR 141.62))
Nuisance level
2 mg/L
Missouri level
4 mg/L
CAS number
16984-48-8

Check your fluoride number

Type the value from your lab report. It is compared to the EPA limit, the same way the full interpretation does it.

Test your own well for fluoride

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209Already tested? Upload the report

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Systems that remove fluoride

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For fluoride

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For fluoride

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.

Where fluoride is worst, by homeowner tests

Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.

CountyAbove state levelWells testedHighest
Lincoln County, Missouri100
Henry County, Missouri62
Pike County, Missouri39
Hancock County, Maine2,937
Montgomery County, Missouri60
Iron County, Missouri62
St. Francois County, Missouri265
Madison County, Missouri503
Oxford County, Maine1,468
Franklin County, Maine899
St. Charles County, Missouri55
Carroll County, New Hampshire1,91015 mg/L
Lewis County, Missouri116
Livingston County, Missouri33
York County, Maine2,695

By individual samples

Counties with at least 30 individual samples in public monitoring data, against the EPA limit.

CountyAbove EPA limitSamplesDetectedMedian
Lynn County, Texas44100%5.03 mg/L
Terry County, Texas66100%4.54 mg/L
Dawson County, Texas107100%4.55 mg/L
Comanche County, Oklahoma57100%7.44 mg/L
Sweetwater County, Wyoming320100%5.2 mg/L
Gaines County, Texas97100%4 mg/L
Horry County, South Carolina29098%4 mg/L
Rio Blanco County, Colorado39099%3.3 mg/L
Humphreys County, Tennessee3491%1.4 mg/L
Briscoe County, Texas33100%3.7 mg/L
Hockley County, Texas39100%3.84 mg/L
Martin County, Texas87100%3.2 mg/L
Yoakum County, Texas92100%3.56 mg/L
Lubbock County, Texas90100%3.25 mg/L
Adams County, North Dakota102100%2.7 mg/L

How to test

Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure fluoride at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.

How to treat

  • Point-of-use reverse osmosis
  • Activated alumina
  • Distillation