Nitrate is widespread in Yakima County wells.
1 widespread, 2 rare out of 3 health checks.
From 234 wells tested in Yakima County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: arsenic (2), uranium (2), radon (2), lead (2).
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 70,576 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Yakima County compares with Washington and the counties around it.
Each result puts Yakima County next to the 8 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Yakima County wells.
Nitrate68 of 224 wells over
Too few tested to show: Benton, Kittitas, Klickitat, Lewis, Skamania.
These 2 are rare in Yakima County.
Fluoride2 of 62 wells over
Too few tested to show: Benton, Klickitat, Lewis, Skamania.
Manganese1 of 36 wells over
Too few tested to show: Benton, King, Klickitat, Lewis, Skamania.
Too few Yakima County wells were tested for these 4.
Arsenic2 wells tested
Uranium2 wells tested
Radon in water2 wells tested
Lead2 wells tested
None of the 2 Yakima County wells tested for bacteria had it, but every well needs a yearly test.
Coliform bacteria0 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 Yakima County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 7 of 44 tested wells, and it isn't a health risk.
Iron stains7 of 44 wells had it
Too few tested to show: Benton, King, Klickitat, Lewis, Skamania.
Yakima County has 234 tested wells, and the busiest decade for testing was the 2010s.
Only 26 of the 234 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Yakima 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 3 things to check in Yakima County.
- Bacteria
- Nitrate
- Arsenic
What Washington offers well owners
- Free testingDOH offers free nitrate and coliform testing to eligible well owners in parts of the Lower Yakima Valley and Western Benton County. See the program
- Certified labsWashington's list of certified labs
- Well recordsWashington's well record search
Here's what we know about radon and PFAS in Yakima County.
Yakima 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 13 town water systems in Yakima County test for PFAS. None found any. No well in Yakima 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 Yakima County
Is well water in Yakima County safe to drink?
68 of 224 wells tested in Yakima County had nitrate over the limit, about 3 in 10. Across Washington it's about 2 in 10. That's a bigger share than in 14 of the 15 other Washington counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated. So test your own well for nitrate before you count on it.
Can I get my well tested for free in Yakima County?
DOH offers free nitrate and coliform testing to eligible well owners in parts of the Lower Yakima Valley and Western Benton County. If not, use a lab Washington has certified for drinking water. Ask for bacteria, nitrate and arsenic, the tests that matter most in Yakima County.
How does Yakima County compare with the counties around it?
For nitrate, the share of tested wells over the limit: Yakima County, at 30%, had a higher share than all 3 neighboring counties with data. Groundwater doesn't stop at county lines, so Grant's 23% is worth knowing about if you live near it.
How often should I test my well in Yakima County?
None of the 2 wells tested for bacteria in Yakima County had it, but the CDC still says to 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 Yakima County numbers come from
- People on wells: 70,576 in Yakima County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 2,468 well water samples from 234 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2022.
- Neighboring counties: the 8 counties that share a border with Yakima County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 13 town water systems in Yakima County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Yakima County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Department of Health (DOH); Department of Ecology for well records and lab accreditation, checked November 1, 2026.