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 nitrate.
Washington's private well pageNitrate in Washington well water, by county
Nitrate is widespread, over the limit in 15% or more of tested wells, in 4 of the 17 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 2 in 10 tested wells had nitrate over the EPA limit of 10 mg/L (165 of 1,070). Across all tested wells in the US it's about 1 in 12. So nitrate turns up in Washington wells about twice as often as in the country as a whole, and a test is worth adding even if your county isn't on the list below.
Why it matters: It's dangerous for babies under 6 months, because it keeps their blood from carrying enough oxygen.
Nitrate soaks down into groundwater from fertilizer, manure and septic systems.
Nitrate in tested wells, county by county
Share of each county's tested wells with at least one result over the EPA limit of 10 mg/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 |
|---|---|---|---|
| Whatcom County | 104 | Widespread | |
| Franklin County | 28 | Widespread | |
| Yakima County | 224 | Widespread | |
| Grant County | 48 | Widespread | |
| Adams County | 10 | Widespread | |
| Pierce County | 16 | Worth checking | |
| Thurston County | 203 | Rare | |
| Okanogan County | 96 | Rare | |
| Stevens County | 117 | Rare | |
| Kitsap County | 68 | Rare | |
| King County | 32 | Rare | |
| Snohomish County | 19 | Rare | |
| Spokane County | 18 | Rare | |
| Mason County | 17 | Rare | |
| Douglas County | 11 | Rare | |
| Whitman County | 11 | Rare | |
| Ferry County | 10 | Rare |
* Likely overstated. These shares come from a narrow set of wells, so they probably run high for the county as a whole:
- Whatcom County: Almost all of these tests come from the US Geological Survey in one small part of the county, so this likely overstates it.
13 more Washington counties have 1 to 9 tested wells for nitrate, too few to rate.
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Where to get your well tested for nitrate in Washington
A lab Washington certifies
Ask for nitrate 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 nitrate.
Compare kitsKeep reading about wells in Washington
- Well water testing in Washington: how to get tested and what turns up statewide
- Nitrate in well water: where it comes from, what it does and how to remove it
- Arsenic 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 nitrate in Washington
Is there nitrate in Washington well water?
Nitrate is widespread, over the limit in 15% or more of tested wells, in 4 of the 17 Washington counties with 10 or more tested wells. 1 more look high, but those results likely overstate it. Across Washington, about 2 in 10 tested wells had nitrate over the EPA limit of 10 mg/L (165 of 1,070). Across all tested wells in the US it's about 1 in 12. So nitrate turns up in Washington wells about twice as often as in the country as a whole, and a test is worth adding even if your county isn't on the list below.
Where can I get my well tested for nitrate 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 nitrate 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 mg/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.