Manganese and arsenic are worth checking in Thurston County wells.
2 worth checking, 3 rare out of 5 health checks.
From 203 wells tested in Thurston County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (7).
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 6 people 48,744 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Less likely, but the EPA still says test your air.
Radon zones: EPA map
Here's how Thurston County compares with Washington and the counties around it.
Each result puts Thurston County next to the 4 counties that border it, on the chart's 0 to 50% scale.
These 2 are worth checking in Thurston County.
Manganese9 of 99 wells over
Too few tested to show: Grays Harbor, Lewis.
Arsenic2 of 35 wells over
Too few tested to show: Grays Harbor, Lewis, Mason.
These 3 are rare in Thurston County.
Nitrate5 of 203 wells over
Too few tested to show: Grays Harbor, Lewis.
Lead0 of 35 wells over
Too few tested to show: Grays Harbor, Lewis, Mason.
Too few Thurston County wells were tested for this one.
Uranium7 wells tested
Coliform bacteria turned up in 34 of 78 tested Thurston County wells, so test for it every year.
Coliform bacteria34 of 78 wells had it
E. coli0 of 23 wells had it
E. coli means human or animal waste is getting in, so if a test of your Thurston County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 42 of 99 tested wells, and it isn't a health risk.
Iron stains42 of 99 wells had it
Too few tested to show: Grays Harbor, Lewis.
About 3 in 10 of the 203 wells tested in Thurston County have a test from 2020 or later.
With 66 wells tested since 2020, age matters less here than who did the testing and why.
Most Thurston 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 Thurston County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Washington offers well owners
- Free testingDOH offers free nitrate and coliform testing to eligible well owners in parts of the Lower Yakima Valley and Western Benton County. See the program
- Certified labsWashington's list of certified labs
- Well recordsWashington's well record search
Here's what we know about radon and PFAS in Thurston County.
Thurston County is in the EPA's lowest radon zone, so radon from well water is unlikely to be a problem. Radon guide
Between 2023 and 2025 the EPA had 7 town water systems in Thurston County test for PFAS. 1 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 5.8 ng/L of PFOS. No well in Thurston 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 Thurston County
Is well water in Thurston County safe to drink?
9 of 99 wells tested in Thurston County had manganese over the limit, about 1 in 11. Across Washington it's about 2 in 10. That's a bigger share than in 10 of the 15 other Washington counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated. So test your own well for manganese before you count on it.
Can I get my well tested for free in Thurston County?
DOH offers free nitrate and coliform testing to eligible well owners in parts of the Lower Yakima Valley and Western Benton County. If not, use a lab Washington has certified for drinking water. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Thurston County.
How does Thurston County compare with the counties around it?
For manganese, the share of tested wells over the limit: Thurston County, at 9%, had a higher share than all 2 neighboring counties with data. Groundwater doesn't stop at county lines, so Pierce's 2% is worth knowing about if you live near it.
How often should I test my well in Thurston County?
In Thurston County, 34 of 78 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 Thurston County numbers come from
- People on wells: 48,744 in Thurston County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 3,698 well water samples from 203 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2026.
- Neighboring counties: the 4 counties that share a border with Thurston County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 7 town water systems in Thurston County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Thurston County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: Department of Health (DOH); Department of Ecology for well records and lab accreditation, checked November 1, 2026.