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Health problems are rare in tested Ravalli County wells.

All 7 health checks came back rare here.

From 25 wells tested in Ravalli County since 2001; your own well needs its own test. How to read this

Tested wells over the limit RavalliMontana
Manganese0%0 of 22Arsenic0%0 of 18Radon0%0 of 18Uranium0%0 of 18Nitrate0%0 of 21Fluoride0%0 of 22Lead0%0 of 18
GermsTest every year, whatever the chart says
Coliform bacteria0%0 of 4E. coli0%0 of 4
StainsNot a health risk
Iron stains6%1 of 18

Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+

Lab results: Water Quality Portal (USGS and EPA)

Who drinks from a well here

8 in 10 people 33,358 people

Nobody else tests these wells. Only you do.

People on wells: EPA researchers' 2020 estimate

How deep wells go here

76 ft Near the surface: fertilizer, germs Deeper: arsenic, uranium from rock 200 ft

Middle depth: some shelter from the surface, not complete.

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 Ravalli County compares with Montana and the counties around it.

Each result puts Ravalli County next to the 6 counties that border it, on the chart's 0 to 50% scale.

All 7 health checks are rare in Ravalli County.

Manganese0 of 22 wells over

None of the 22 wells tested here from 2001 to 2010 were over the EPA health advisory of 0.3 mg/L, against about 1 in 3 across Montana. Ravalli County had none, while 9 of the 13 other Montana counties with 10 or more tested wells had at least one, leaving out 4 counties whose results are likely overstated.

Ravalli and its neighbors
Deer Lodge64%
Idaho, ID0%
Lemhi, ID0%
Ravalli0%

Too few tested to show: Beaverhead, Granite, Missoula.

Manganese guide

Arsenic0 of 18 wells over

None of the 18 wells tested here in 2001 were over the EPA limit of 10 µg/L, against about 2 in 10 across Montana. Half the results were under 0.5 µg/L, and the top 1 in 10 were 3.9 µg/L or more. Ravalli County had none, while 5 of the 9 other Montana counties with 10 or more tested wells had at least one, leaving out 7 counties whose results are likely overstated.

Ravalli and its neighbors
Idaho, ID6%
Lemhi, ID4%
Ravalli0%

* Likely overstated, so we don't rank it.

Too few tested to show: Beaverhead, Deer Lodge, Granite, Missoula.

Arsenic guide

Radon in water0 of 18 wells over

None of the 18 wells tested here in 2001 were over 4,000 pCi/L, a level the EPA proposed, against about 2 in 10 across Montana. Half the results were under 1,360 pCi/L, and the top 1 in 10 were 2,130 pCi/L or more. Ravalli County had none, while 3 of the 4 other Montana counties with 10 or more tested wells had at least one.

Radon guide

Uranium0 of 18 wells over

None of the 18 wells tested here in 2001 were over the EPA limit of 30 µg/L, against about 1 in 12 across Montana. Half the results were under 0.69 µg/L, and the top 1 in 10 were 6.3 µg/L or more. Ravalli County had none, while 5 of the 10 other Montana counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Uranium guide

Nitrate0 of 21 wells over

None of the 21 wells tested here from 2001 to 2022 were over the EPA limit of 10 mg/L, against about 1 in 13 across Montana. Half the results were under 0.07 mg/L, and the top 1 in 10 were 0.84 mg/L or more. Ravalli County had none, while 8 of the 13 other Montana counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Ravalli and its neighbors
Idaho, ID0%
Lemhi, ID0%
Ravalli0%

Too few tested to show: Beaverhead, Deer Lodge, Granite, Missoula.

Nitrate guide

Fluoride0 of 22 wells over

None of the 22 wells tested here from 2001 to 2010 were over the EPA limit of 4 mg/L, against about 1 in 19 across Montana. Half the results were under 0.2 mg/L, and the top 1 in 10 were 0.46 mg/L or more. Ravalli County had none, while 6 of the 14 other Montana counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Ravalli and its neighbors
Lemhi, ID4%
Idaho, ID0%
Ravalli0%

Too few tested to show: Beaverhead, Deer Lodge, Granite, Missoula.

Lead0 of 18 wells over

None of the 18 wells tested here in 2001 were over the EPA action level of 15 µg/L, against about 1 in 24 across Montana. At least half the results were too low for the lab to measure, and the top 1 in 10 were 0.19 µg/L or more. Ravalli County had none, while 5 of the 15 other Montana counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Ravalli and its neighbors
Idaho, ID0%
Ravalli0%

Too few tested to show: Beaverhead, Deer Lodge, Granite, Lemhi, ID, Missoula.

Lead guide

None of the 4 Ravalli County wells tested for bacteria had it, but every well needs a yearly test.

Coliform bacteria0 of 4 wells had it

None of the 4 wells tested here in 2010 had coliform bacteria, against about 3 in 10 across Montana.

Bacteria guide

E. coli0 of 4 wells had it

None of the 4 wells tested here in 2010 had E. coli, against about 1 in 30 across Montana.

E. coli means human or animal waste is getting in, so if a test of your Ravalli County well finds it, boil drinking water until the well is fixed.

Bacteria guide

Iron reached staining levels in 1 of 18 tested wells, and it isn't a health risk.

Iron stains1 of 18 wells had it

1 of 18 wells tested here in 2001 had enough iron to stain (0.3 mg/L), against about 1 in 3 across Montana.

Ravalli and its neighbors
Deer Lodge64%
Idaho, ID11%
Ravalli6%
Lemhi, ID0%

Too few tested to show: Beaverhead, Granite, Missoula.

Iron guide

Most of the 25 wells tested in Ravalli County were last tested before 2010.

18 wells had a test in the 2000s, 4 in the 2010s and 3 since 2020.

An old result shows the water as it was then, so treat these 25 wells as a starting point and test your own.

Most Ravalli 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 3 things to check in Ravalli County.

  • Bacteria
  • Nitrate
  • Arsenic

What Montana offers well owners

Half the household wells here are shallower than 76 feet.

That comes from 18,009 household wells in Montana's drilling records. Most wells of every kind here are 40 to 144 feet deep. Wells as deep as Ravalli 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 are shallower than in 43 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 Ravalli County.

Ravalli 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 2 town water systems in Ravalli County test for PFAS. 1 found some PFAS, all below the new limits. No well in Ravalli 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

Other counties in Montana
FlatheadGallatinLewis and ClarkYellowstone

All of Montana

Get a yearly reminder to test your Ravalli County well

We'll email you a copy of this page now and one reminder a year. Nothing else. Privacy

Questions people ask about well water in Ravalli County

Is well water in Ravalli County safe to drink?

Most tested wells in Ravalli County came in under the limits. Of 7 health checks with enough tests, nitrate came closest, at 0 of 21 wells over. Every well is different, so test yours for bacteria, nitrate and arsenic.

Can I get my well tested for free in Ravalli 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 and arsenic, the tests that matter most in Ravalli County.

How deep are wells in Ravalli County?

Half the household wells here are shallower than 76 feet. Typical household wells here are shallower than in 43 of the 55 other Montana counties with enough drilling records.

How does Ravalli County compare with the counties around it?

For manganese, the share of tested wells over the limit: 1 of the 3 neighboring counties with data had a higher share than Ravalli County, at 0%. Deer Lodge had the most, at 64%. Groundwater doesn't stop at county lines, so Deer Lodge's 64% is worth knowing about if you live near it.

How often should I test my well in Ravalli County?

None of the 4 wells tested for bacteria in Ravalli County had it, but the CDC still says to test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.

By the Tested Water teamData from the USGS, EPA and Department of Environmental QualityUpdated November 8, 2026

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Where the Ravalli County numbers come from

  • People on wells: 33,358 in Ravalli County, from EPA estimates built on the 2020 Census (Murray et al.).
  • Lab tests: 174 well water samples from 25 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2022.
  • Well depths: 18,009 Montana drilling records for Ravalli County, gathered in the US Groundwater Well Database (Lin and others, 2024).
  • Neighboring counties: the 6 counties that share a border with Ravalli County, from the Census Bureau's county adjacency file.
  • PFAS: EPA tests of 2 town water systems in Ravalli County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
  • Radon: Ravalli County is zone 1 on the EPA Map of Radon Zones.
  • State programs and links: Department of Environmental Quality, checked November 1, 2026.
Download this county's data (CSV)How we read these numbersReport an error
Test for bacteria and nitrate every yearSee lab tests