Manganese is widespread in Clackamas County wells.
1 widespread, 4 rare out of 5 health checks.
From 37 wells tested in Clackamas County since 2001; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: fluoride (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 4 people 97,087 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)
Less likely, but the EPA still says test your air.
Radon zones: EPA map
Here's how Clackamas County compares with Oregon and the counties around it.
Each result puts Clackamas County next to the 6 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Clackamas County wells.
Manganese11 of 35 wells over
Too few tested to show: Hood River.
These 4 are rare in Clackamas County.
Arsenic1 of 36 wells over
Too few tested to show: Hood River.
Lead1 of 36 wells over
Too few tested to show: Hood River.
Nitrate0 of 36 wells over
Too few tested to show: Hood River.
Uranium0 of 34 wells over
Too few tested to show: Hood River.
Too few Clackamas County wells were tested for this one.
Fluoride7 wells tested
Coliform bacteria turned up in 7 of 23 tested Clackamas County wells, so test for it every year.
Coliform bacteria7 of 23 wells had it
Too few tested to show: Hood River, Multnomah, Wasco, Washington.
E. coli0 of 24 wells had it
Too few tested to show: Hood River, Multnomah, Wasco, Washington.
E. coli means human or animal waste is getting in, so if a test of your Clackamas County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 15 of 35 tested wells, and it isn't a health risk.
Iron stains15 of 35 wells had it
Too few tested to show: Hood River.
Clackamas County has 37 tested wells, and the busiest decade for testing was the 2010s.
Only 4 of the 37 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Clackamas 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 Clackamas 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 218 feet.
That comes from 4,670 household wells in Oregon's drilling records. Most wells of every kind here are 40 to 277 feet deep. Wells as deep as Clackamas 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 30 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 Clackamas County.
Clackamas 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 15 town water systems in Clackamas 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 7.0 ng/L of PFOS. No well in Clackamas 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 Clackamas County
Is well water in Clackamas County safe to drink?
11 of 35 wells tested in Clackamas County had manganese over the limit, about 3 in 10. Across Oregon it's about 2 in 10. That's a bigger share than in 16 of the 25 other 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 Clackamas 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 Clackamas County.
How deep are wells in Clackamas County?
Half the household wells here are shallower than 218 feet. Typical household wells here go deeper than in 30 of the 35 other Oregon counties with enough drilling records.
How does Clackamas County compare with the counties around it?
For manganese, the share of tested wells over the limit: 4 of the 5 neighboring counties with data had a higher share than Clackamas County, at 31%. Washington had the most, at 81%. Groundwater doesn't stop at county lines, so Washington's 81% is worth knowing about if you live near it.
How often should I test my well in Clackamas County?
In Clackamas County, 7 of 23 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 Clackamas County numbers come from
- People on wells: 97,087 in Clackamas County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 421 well water samples from 37 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2022.
- Well depths: 4,670 Oregon drilling records for Clackamas County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with Clackamas County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 15 town water systems in Clackamas County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Clackamas County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: Oregon Health Authority, checked November 1, 2026.