Well water in Yakima County, Washington
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Testing strongly recommended
tested well samples in Yakima County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
The strongest signal is PFOA: 91% of 11 local samples were above the limit, too few samples to carry the headline but first on the test list below.
8,504 test results across 15 contaminants from at least 1,203 wells, 1939 to 2025; nitrate has the most at 3,681. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 62,059 people in Yakima County get their drinking water from a private well, per USGS 2015 county water use. That is about 25% of residents.
Separately, the USGS national arsenic model estimates that 11% of the 62,059 people on private wells in Yakima County draw water above 10 ug/L (the model's range is 9% to 14%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Yakima County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| PFOA 2025 | 11 | 91% | 37 | 200 | 4 ng/L EPA limit | |
| PFOS 2025 | 11 | 91% | 800 | 4,500 | 4 ng/L EPA limit | |
| Nitrate 1939 to 2024 | 3,681 | 90% | 3.93 | 434 | 10 mg/L EPA limit | |
| Lead 1970 to 2016 | 85 | 54% | 0 | 200 | 15 ug/L EPA limit | |
| Arsenic 1968 to 2016 | 73 | 74% | 4 | 50 | 10 ug/L EPA limit | |
| Fluoride 1939 to 2024 | 1,152 | 69% | 0.2 | 6.08 | 4 mg/L EPA limit | |
| Copper 1970 to 2016 | 131 | 82% | 0.02 | 0.39 | 1.3 mg/L EPA limit | |
| Chloride 1939 to 2024 | no limit | 1,203 | 99% | 15 | 201 | 250 mg/L nuisance level |
| Sodium 1939 to 2024 | no limit | 1,195 | 100% | 38.2 | 203 | 20 mg/L health guideline |
| Iron 1939 to 2024 | no limit | 496 | 65% | 9.6 | 16,400 | 300 ug/L nuisance level |
| Manganese 1951 to 2024 | no limit | 447 | 63% | 0.46 | 3,200 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (8), Radium (226 + 228) (4), Uranium (2), Radon (5).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | 8%1,665 samples | 31%222 samples | 39%1,628 samples | 75%166 samples |
| Fluoride | 0%364 samples | 1%88 samples | <1%575 samples | 0%125 samples |
Nitrate above the limit in Yakima County rose from 39% of 1628 samples in the 2010s to 75% of 166 in the 2020s.
Fluoride has held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are pfoa (91% of 11 samples), pfos (91% of 11 samples), and nitrate (26% of 3,681 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Yakima County
- 1PFOA91% of 11 local samples were above the limit.
- 2PFOS91% of 11 local samples were above the limit.
- 3Nitrate26% of 3,681 local samples were above the limit.
- 4Lead5% of 85 local samples were above the limit.
- 5Arsenic1% of 73 local samples were above the limit.
- 6Fluoride<1% of 1,152 local samples were above the limit.
- 7Coliform bacteriaRecommended for every private well, every year.
- 8Volatile organic compounds (VOCs)13 reported spills and releases on record locally.
Test your Yakima County well for PFOA, PFOS and nitrate
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Washington: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Yakima County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Yakima County
8,473 domestic wells in Yakima County are on record with the state since 1981. the typical well is 185 feet deep (one in ten goes past 465 feet).
In a typical Yakima County well, the median yield is 60 gallons per minute, 3% of wells yield under 3 gallons per minute and usually need a storage tank.
Find your own well's report
The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.
- Open Ecology well report search and choose Water Well.
- It lists depth, casing, static water level, the yield test and the driller.
Washington has required well reports since 1971; reports are located only to the quarter-quarter section, so check the address on the scan.
The rock under Yakima County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Washington
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Drinking Water, Washington State Department of Health
- Environmental lab accreditation, Washington State Department of Ecology
Contamination sources on record in Yakima County
Washington Ecology facility interactions records 13 reported spills and releases in Yakima County, among 1,780 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 13
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 1,719
- other remediation projects
- 48
- other solid waste facilities
Treatment that fits the local profile
PFOA
Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
PFOS
Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For PFOA
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For PFOA
Whole-house PFAS carbon system
whole-house, at the point of entry, about $3,000
Granular activated carbon certified to NSF/ANSI 53 for PFOA and PFOS; replace media on schedule.
For PFOA
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For PFOS
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For PFOS
Aquasana HealthShield whole-house filter
whole-house, at the point of entry, about $2,099
Whole-house carbon system the maker certifies to reduce PFAS (PFOA and PFOS) and VOCs at every tap; a UV option adds bacteria protection.
For lead
Acid neutralizing filter
whole-house, at the point of entry, about $1,200
Raises pH so plumbing stops leaching lead and copper.
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Common questions
How deep are wells in Yakima County?
The typical domestic well in Yakima County is 185 feet deep, based on 8,473 wells reported to the state since 1981. One in ten is deeper than 465 feet.
Is there arsenic in well water in Yakima County?
Arsenic was detected in 74% of 73 public well samples in Yakima County, and 1% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How often should I test a private well in Yakima County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Yakima County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Washington dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 8,504 samples in Yakima County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 62,059 people on private wells in Yakima County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- Washington Ecology well construction reports: 8,477 well records in Yakima County, 8,473 domestic. Well construction reports filed with the Washington State Department of Ecology, water wells only, located at the quarter-quarter section. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 17, 2026.
- Washington Ecology facility interactions: 1,780 regulated sites located in Yakima County. Toxics cleanup sites, spills and solid waste facilities from the Washington State Department of Ecology Facility/Site register. Retrieved September 17, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.