Free testing, with limits
Free nitrate and bacteria testing in Washington is limited to parts of the Lower Yakima Valley and western Benton County. Check which tests it includes before you count on it for arsenic.
Washington's private well pageArsenic in Washington well water, by county
Arsenic is widespread, over the limit in 15% or more of tested wells, in 6 of the 15 Washington counties with 10 or more tested wells. 1 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.
How Washington compares with the rest of the country
Across Washington, about 1 in 7 tested wells had arsenic over the EPA limit of 10 µg/L (63 of 456). Across all tested wells in the US it's about 1 in 9. Washington 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%.
| County | Wells tested | Wells over the limit | Level |
|---|---|---|---|
| Grant County | 38 | Widespread | |
| King County | 29 | Widespread | |
| Franklin County | 28 | Widespread | |
| Whatcom County | 34 | Widespread | |
| Ferry County | 10 | Widespread | |
| Okanogan County | 44 | Widespread | |
| Kitsap County | 20 | Widespread | |
| Stevens County | 85 | Worth checking | |
| Adams County | 10 | Worth checking | |
| Thurston County | 35 | Worth checking | |
| Clark County | 30 | Rare | |
| Spokane County | 24 | Rare | |
| Kittitas County | 20 | Rare | |
| Pierce County | 16 | Rare | |
| Whitman County | 11 | Rare |
* Likely overstated. These shares come from a narrow set of wells, so they probably run high for the county as a whole:
- Kitsap County: All of these tests come from the US Geological Survey in one small part of the county, so it may not match the rest of the county.
10 more Washington counties have 1 to 9 tested wells for arsenic, too few to rate.
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Where to get your well tested for arsenic in Washington
A lab Washington certifies
Ask for arsenic by name. Results from a certified lab count for a home sale or a loan.
Labs certified by WashingtonA mail-in kit
Fill the bottles at your kitchen tap and mail them back. We mark the kits that include arsenic.
Compare kitsKeep reading about wells in Washington
- Well water testing in Washington: how to get tested and what turns up statewide
- Arsenic in well water: where it comes from, what it does and how to remove it
- Nitrate in Washington wells, by county
- Uranium in Washington wells, by county
- Manganese in Washington wells, by county
- Lead in Washington wells, by county
- Radon in Washington wells, by county
Questions people ask about arsenic in Washington
Is there arsenic in Washington well water?
Arsenic is widespread, over the limit in 15% or more of tested wells, in 6 of the 15 Washington counties with 10 or more tested wells. 1 more look high, but those results likely overstate it. Across Washington, about 1 in 7 tested wells had arsenic over the EPA limit of 10 µg/L (63 of 456). Across all tested wells in the US it's about 1 in 9. Washington 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 Washington?
Free nitrate and bacteria testing in Washington is limited to parts of the Lower Yakima Valley and western Benton County. If that doesn't cover you, use a lab certified by Washington for drinking water, or a mail-in kit that includes arsenic from a certified lab.
See Washington'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: Department of Health (DOH); Department of Ecology for well records and lab accreditation.