Manganese has turned up often in Flathead County wells, mostly in older study samples.
1 likely overstated, 2 rare out of 3 health checks.
From 21 wells tested in Flathead County since 2009; your own well needs its own test. How to read this
*Manganese: Most of these tests come from one small part of the county, mostly before 2013, so this likely overstates it.
Not charted, because fewer than 10 wells were tested: nitrate (1), uranium (1), radon (1), fluoride (2).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
1 in 2 people 47,064 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Flathead County compares with Montana and the counties around it.
Each result puts Flathead County next to the 9 counties that border it, on the chart's 0 to 50% scale.
This one has turned up often here, mostly in older study samples.
Manganese3 of 19 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Lake, Lincoln, Missoula, Pondera, Sanders, Teton.
Most of these tests come from one small part of the county, mostly before 2013, so this likely overstates it.
These 2 are rare in Flathead County.
Arsenic0 of 18 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Lake, Lincoln, Missoula, Pondera, Sanders, Teton.
Lead0 of 18 wells over
Too few tested to show: Lake, Lincoln, Missoula, Pondera, Sanders, Teton.
Too few Flathead County wells were tested for these 4.
Nitrate1 well tested
Uranium1 well tested
Radon in water1 well tested
Fluoride2 wells tested
Coliform bacteria turned up in 5 of 21 tested Flathead County wells, so test for it every year.
Coliform bacteria5 of 21 wells had it
Too few tested to show: Glacier, Lake, Lewis and Clark, Lincoln, Missoula, Pondera, Sanders, Teton.
E. coli0 of 21 wells had it
E. coli means human or animal waste is getting in, so if a test of your Flathead County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 3 of 18 tested wells, and it isn't a health risk.
Iron stains3 of 18 wells had it
Too few tested to show: Lake, Lincoln, Missoula, Pondera, Sanders, Teton.
Flathead County has 21 tested wells, and the busiest decade for testing was the 2000s.
None of the 21 wells has a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Flathead County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 4 things to check in Flathead County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Montana offers well owners
- Free testingDPHHS offers free well water testing to prospective or licensed childcare facilities. See the program
- Certified labsMontana's list of certified labs
- Well recordsWe didn't find an online search.
Half the household wells here are shallower than 193 feet.
That comes from 17,055 household wells in Montana's drilling records. Most wells of every kind here are 102 to 293 feet deep. Wells as deep as Flathead County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here go deeper than in 50 of the 55 other Montana counties with enough drilling records.
How to find your own well's depth
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Flathead County.
Flathead County is in the EPA's highest radon zone. Radon from well water adds to the radon in your indoor air, so test your air first, and your water too if the air is high. Radon guide
Between 2023 and 2025 the EPA had 6 town water systems in Flathead County test for PFAS. 2 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 6.6 ng/L of PFOS. No well in Flathead County has public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Flathead County
Is well water in Flathead County safe to drink?
3 of 19 wells tested in Flathead County had manganese over the limit, about 2 in 10. Across Montana it's about 1 in 3. We don't rank this against other Montana counties, because most of these tests are old study samples. Most of these tests come from one small part of the county, mostly before 2013, so this likely overstates it. So test your own well for manganese before you count on it.
Can I get my well tested for free in Flathead County?
DPHHS offers free well water testing to prospective or licensed childcare facilities. If not, use a lab Montana has certified for drinking water. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Flathead County.
How deep are wells in Flathead County?
Half the household wells here are shallower than 193 feet. Typical household wells here go deeper than in 50 of the 55 other Montana counties with enough drilling records.
How does Flathead County compare with the counties around it?
For manganese, the share of tested wells over the limit: 2 of the 3 neighboring counties with data had a higher share than Flathead County, at 16%. Powell had the most, at 44%. Groundwater doesn't stop at county lines, so Powell's 44% is worth knowing about if you live near it.
How often should I test my well in Flathead County?
In Flathead County, 5 of 21 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Flathead County numbers come from
- People on wells: 47,064 in Flathead County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 284 well water samples from 21 wells in the Water Quality Portal, run by the USGS and EPA, 2009 to 2014.
- Well depths: 17,055 Montana drilling records for Flathead County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 9 counties that share a border with Flathead County, from the Census Bureau's county adjacency file.
- Results marked likely overstated: our own check of who tested the wells, when and where.
- PFAS: EPA tests of 6 town water systems in Flathead County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Flathead County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Environmental Quality, checked November 1, 2026.