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Arsenic in Oregon well water, by county

By the Tested Water teamLab data from the USGS and EPA Water Quality Portal, 2000 to 2026Updated November 8, 2026

Arsenic is widespread, over the limit in 15% or more of tested wells, in 8 of the 26 Oregon counties with 10 or more tested wells. 2 more look high, but those results likely overstate it. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.

Find an arsenic test See every county

How Oregon compares with the rest of the country

Across Oregon, about 1 in 8 tested wells had arsenic over the EPA limit of 10 µg/L (227 of 1,767). Across all tested wells in the US it's about 1 in 9. Oregon is about average, so the county you live in tells you more than the state does.

Why it matters: Drinking it for years raises the risk of skin, bladder and lung cancer.

Arsenic dissolves out of certain rocks and old sediments, so it can be high even where nobody has polluted anything.

Arsenic in tested wells, county by county

Share of each county's tested wells with at least one result over the EPA limit of 10 µg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.

CountyWells testedWells over the limitLevel
Malheur County 48
94%* 45 of 48
 Widespread
Gilliam County 29
48%* 14 of 29
 Widespread
Lincoln County 23
35% 8 of 23
 Widespread
Washington County 27
33% 9 of 27
 Widespread
Harney County 91
30% 27 of 91
 Widespread
Wasco County 13
23% 3 of 13
 Widespread
Benton County 25
20% 5 of 25
 Widespread
Morrow County 76
20% 15 of 76
 Widespread
Multnomah County 44
18% 8 of 44
 Widespread
Marion County 77
17% 13 of 77
 Widespread
Douglas County 159
13% 20 of 159
 Worth checking
Clatsop County 49
12% 6 of 49
 Worth checking
Yamhill County 69
9% 6 of 69
 Worth checking
Columbia County 14
7%* 1 of 14
 Worth checking
Umatilla County 236
7% 16 of 236
 Worth checking
Coos County 30
7% 2 of 30
 Worth checking
Jackson County 168
7% 11 of 168
 Worth checking
Klamath County 130
6% 8 of 130
 Worth checking
Clackamas County 36
3% 1 of 36
 Rare
Josephine County 37
3% 1 of 37
 Rare
Deschutes County 139
0% 0 of 139
 Rare
Lane County 86
0% 0 of 86
 Rare
Linn County 45
0% 0 of 45
 Rare
Tillamook County 40
0% 0 of 40
 Rare
Polk County 22
0% 0 of 22
 Rare
Crook County 11
0% 0 of 11
 Rare

* Likely overstated. These shares come from a narrow set of wells, so they probably run high for the county as a whole:

  • Malheur County: All of these tests come from Oregon's environment department in one small part of the county, so this likely overstates it.
  • Gilliam County: Almost all of these tests come from Oregon's environment department in one small part of the county, so it may not match the rest of the county.
  • Columbia County: All of these tests come from Oregon's environment department in one small part of the county, so it may not match the rest of the county.

10 more Oregon counties have 1 to 9 tested wells for arsenic, too few to rate.

Download this table (CSV) · Free to reuse under CC BY 4.0

Where to get your well tested for arsenic in Oregon

1

Your county health department

Oregon doesn't run a statewide free testing program that we know of. Some county health departments test wells or sell kits, so call yours first.

Oregon's private well page
2

A lab Oregon certifies

Ask for arsenic by name. Results from a certified lab count for a home sale or a loan.

Labs certified by Oregon
3

A mail-in kit

Fill the bottles at your kitchen tap and mail them back. We mark the kits that include arsenic.

Compare kits

Keep reading about wells in Oregon

Questions people ask about arsenic in Oregon

Is there arsenic in Oregon well water?

Arsenic is widespread, over the limit in 15% or more of tested wells, in 8 of the 26 Oregon counties with 10 or more tested wells. 2 more look high, but those results likely overstate it. Across Oregon, about 1 in 8 tested wells had arsenic over the EPA limit of 10 µg/L (227 of 1,767). Across all tested wells in the US it's about 1 in 9. Oregon is about average, so the county you live in tells you more than the state does.

Where can I get my well tested for arsenic in Oregon?

Use a lab certified by Oregon for drinking water, or a mail-in kit that includes arsenic from a certified lab. Some county health departments test wells too, so call yours first.

See Oregon's list of certified labs, or compare mail-in kits.

Where these numbers come from

  • Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA limit of 10 µg/L. Wells tested for studies and monitoring, not a random sample of homes.
  • Likely overstated: our own check of who tested the wells, when and where. How we check.
  • State programs and links: Oregon Health Authority.