Manganese and arsenic are widespread in Washington County wells.
2 widespread, 3 rare out of 5 health checks.
From 30 wells tested in Washington County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: fluoride (1).
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 11 people 54,269 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)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Washington County compares with Oregon and the counties around it.
Each result puts Washington County next to the 6 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Washington County wells.
Manganese22 of 27 wells over
* Likely overstated, so we don't rank it.
Arsenic9 of 27 wells over
* Likely overstated, so we don't rank it.
These 3 are rare in Washington County.
Uranium1 of 26 wells over
Lead1 of 27 wells over
* Likely overstated, so we don't rank it.
Nitrate1 of 30 wells over
Too few Washington County wells were tested for this one.
Fluoride1 well tested
Coliform bacteria turned up in 2 of 2 tested Washington County wells, so test for it every year.
Coliform bacteria2 of 2 wells had it
E. coli0 of 2 wells had it
E. coli means human or animal waste is getting in, so if a test of your Washington County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 25 of 27 tested wells, and it isn't a health risk.
Iron stains25 of 27 wells had it
Washington County has 30 tested wells, and the busiest decade for testing was the 2010s.
Only 6 of the 30 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Washington 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 Washington County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Oregon offers well owners
- Free testingWe didn't find a free program for all of Oregon. Oregon's private well page
- Certified labsOregon's list of certified labs
- Well recordsOregon's well record search
- New wellsUnder the Domestic Well Testing Act, sellers must test the well for arsenic, nitrate and total coliform bacteria during a real estate transaction and send the results to the buyer and OHA within 90 days.
Half the household wells here are shallower than 190 feet.
That comes from 11,792 household wells in Oregon's drilling records. Most wells of every kind here are 52 to 272 feet deep. Wells as deep as Washington 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 26 of the 35 other Oregon counties with enough drilling records.
Look up your own well's depth in Oregon's well record search, or see how to find it.
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Washington County.
Washington County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 10 town water systems in Washington County test for PFAS. 1 found some PFAS, all below the new limits. No well in Washington 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 Washington County
Is well water in Washington County safe to drink?
22 of 27 wells tested in Washington County had manganese over the limit, about 8 in 10. Across Oregon it's about 2 in 10. That's the highest share among the 26 Oregon counties with 10 or more tested wells, leaving out 2 counties whose results are likely overstated. So test your own well for manganese before you count on it.
Where can I get my well tested in Washington County?
Use a lab Oregon has certified for drinking water. Oregon's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Washington County.
How deep are wells in Washington County?
Half the household wells here are shallower than 190 feet. Typical household wells here go deeper than in 26 of the 35 other Oregon counties with enough drilling records.
How does Washington County compare with the counties around it?
For manganese, the share of tested wells over the limit: Washington County, at 81%, had a higher share than all 6 neighboring counties with data. Groundwater doesn't stop at county lines, so Multnomah's 72% is worth knowing about if you live near it.
How often should I test my well in Washington County?
In Washington County, 2 of 2 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 Washington County numbers come from
- People on wells: 54,269 in Washington County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 485 well water samples from 30 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2025.
- Well depths: 11,792 Oregon drilling records for Washington County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with Washington County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 10 town water systems in Washington County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Washington County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Oregon Health Authority, checked November 1, 2026.