Nitrate is worth checking in Pierce County wells.
1 worth checking, 5 rare out of 6 health checks.
From 58 wells tested in Pierce County since 2000; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 23 people 40,397 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 Pierce County compares with Washington and the counties around it.
Each result puts Pierce County next to the 6 counties that border it, on the chart's 0 to 50% scale.
This one is worth checking in Pierce County.
Nitrate1 of 16 wells over
Too few tested to show: Lewis.
These 5 are rare in Pierce County.
Manganese1 of 58 wells over
Too few tested to show: King, Lewis.
Uranium0 of 16 wells over
Arsenic0 of 16 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Lewis, Mason, Yakima.
Lead0 of 16 wells over
Too few tested to show: Lewis, Mason, Yakima.
Coliform bacteria turned up in 3 of 6 tested Pierce County wells, so test for it every year.
Coliform bacteria3 of 6 wells had it
E. coli0 of 6 wells had it
E. coli means human or animal waste is getting in, so if a test of your Pierce County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 0 of 58 tested wells, and it isn't a health risk.
Iron stains0 of 58 wells had it
Too few tested to show: King, Lewis.
Most of the 58 wells tested in Pierce County were last tested before 2010.
An old result shows the water as it was then, so treat these 58 wells as a starting point and test your own.
Most Pierce 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 Pierce County.
- Bacteria
- Nitrate
- 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 Pierce County.
Pierce 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 31 town water systems in Pierce County test for PFAS. 9 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 154 ng/L of PFOS. No well in Pierce 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 Pierce County
Is well water in Pierce County safe to drink?
1 of 16 wells tested in Pierce County had nitrate over the limit, about 1 in 16. Across Washington it's about 2 in 10. That's a bigger share than in 11 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 nitrate before you count on it.
Can I get my well tested for free in Pierce 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 and arsenic, the tests that matter most in Pierce County.
How does Pierce County compare with the counties around it?
For nitrate, the share of tested wells over the limit: 1 of the 5 neighboring counties with data had a higher share than Pierce County, at 6%. Yakima had the most, at 30%. Groundwater doesn't stop at county lines, so Yakima's 30% is worth knowing about if you live near it.
How often should I test my well in Pierce County?
In Pierce County, 3 of 6 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 Pierce County numbers come from
- People on wells: 40,397 in Pierce County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 344 well water samples from 58 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2016.
- Neighboring counties: the 6 counties that share a border with Pierce County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 31 town water systems in Pierce County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Pierce 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.