Well water in Washington

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Testing strongly recommended

tested well samples in Washington exceeded the EPA limit for uranium (30 ug/L), based on public data from USGS Water Quality Portal.

99,438 test results across 15 contaminants from at least 8,962 wells, 1916 to 2026; chloride has the most at 23,174. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 1,023,853 people in Washington get their drinking water from a private well, per USGS 2015 county water use.

Separately, the USGS national arsenic model estimates that 5% of the 1,023,853 people on private wells in Washington draw water above 10 ug/L (the model's range is 4% to 7%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Washington. 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
Uranium 1980 to 2025	32%	1,440	85%	8.63	123,000	30 ug/L EPA limit
PFOS 2023 to 2025	19%	62	31%	0	4,500	4 ng/L EPA limit
Nitrate 1916 to 2025	18%	19,233	83%	1.4	1,150	10 mg/L EPA limit
PFOA 2023 to 2025	16%	62	24%	0	200	4 ng/L EPA limit
Radium (226 + 228) 1951 to 2025	16%	2,201	91%	0.6	1,060	5 pCi/L EPA limit
Arsenic 1959 to 2026	8%	4,117	81%	1.9	389	10 ug/L EPA limit
E. coli 1998 to 2022	7%	481	7%	0	54	0 MPN/100mL EPA limit
Lead 1959 to 2026	3%	4,270	58%	0.04	770	15 ug/L EPA limit
Fluoride 1938 to 2025	<1%	8,974	82%	0.2	100	4 mg/L EPA limit
Copper 1959 to 2025	<1%	4,492	72%	0.001	8.08	1.3 mg/L EPA limit
Chloride 1916 to 2025	no limit	23,174	98%	9.39	28,900	250 mg/L nuisance level
Sodium 1930 to 2025	no limit	10,587	100%	14	10,500	20 mg/L health guideline
Iron 1916 to 2026	no limit	10,219	79%	30	2,180,000	300 ug/L nuisance level
Manganese 1944 to 2026	no limit	9,424	77%	10	1,430,000	300 ug/L health guideline
Radon 1984 to 2021	no limit	702	96%	480	171,527	2,000 pCi/L health guideline

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	9%12,637 samples	14%1,908 samples	43%4,222 samples	36%466 samples
Fluoride	<1%6,697 samples	<1%1,216 samples	<1%857 samples	0%204 samples
Copper	<1%2,576 samples	<1%902 samples	2%612 samples	3%402 samples
Lead	4%2,156 samples	1%1,078 samples	4%612 samples	2%424 samples
Arsenic	7%2,521 samples	9%1,086 samples	7%261 samples	12%249 samples
Radium (226 + 228)	19%1,095 samples	33%248 samples	6%551 samples	7%307 samples

Nitrate above the limit in Washington fell from 43% of 4222 samples in the 2010s to 36% of 466 in the 2020s.

Arsenic above the limit in Washington rose from 7% of 261 samples in the 2010s to 12% of 249 in the 2020s.

Fluoride, copper, lead, radium (226 + 228) have held within a few points between the two most recent periods with enough samples.

What this means

The contaminants most often above their limit here are uranium (32% of 1,440 samples), pfos (19% of 62 samples), and nitrate (18% of 19,233 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 Washington

1
Uranium
32% of 1,440 local samples were above the limit.
2
PFOS
19% of 62 local samples were above the limit.
3
Nitrate
18% of 19,233 local samples were above the limit.
4
PFOA
16% of 62 local samples were above the limit.
5
Radium (226 + 228)
16% of 2,201 local samples were above the limit.
6
Arsenic
8% of 4,117 local samples were above the limit.
7
E. coli
7% of 481 local samples were above the limit.
8
Volatile organic compounds (VOCs)
981 reported spills and releases on record locally.

Test your Washington well for uranium, 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 $209 Already 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 Washington numbers, $29. Every line explained, ranked by what matters, with the fix for each.

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Send me the Washington report

The numbers above, which tests to order and where, and the treatment that fits the local profile, in one email.

Wells in Washington

163,360 domestic wells in Washington are on record with the state since 1973. the typical well is 157 feet deep (one in ten goes past 420 feet).

In a typical Washington well, the median yield is 20 gallons per minute, 9% of wells yield under 3 gallons per minute and usually need a storage tank.

1970s

1980s

45,846

1990s

62,538

2000s

31,207

2010s

23,198

2020s

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 Washington

Puget Sound aquifer system

Unconsolidated sand and gravel. Wells in sand and gravel are usually shallow and productive, and they recharge quickly from the surface. That makes them the most exposed to nitrate, bacteria and anything spilled nearby, and the least likely to carry arsenic or radon from the rock.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the state 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 Washington

Washington Ecology facility interactions records 981 reported spills and releases in Washington, among 42,904 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.

981: reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
40,414: other remediation projects
1,509: other solid waste facilities

Treatment that fits the local profile

Uranium

Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange

PFOS

Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

PFOA

Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange

Radium (226 + 228)

Water softener (cation exchange); Point-of-use reverse osmosis

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 uranium

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For uranium

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For PFOS

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

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 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 PFOA

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.

Common questions

How deep are wells in Washington?

The typical domestic well in Washington is 157 feet deep, based on 163,360 wells reported to the state since 1973. One in ten is deeper than 420 feet.

Is there arsenic in well water in Washington?

Arsenic was detected in 81% of 4,117 public well samples in Washington, and 8% 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 high is radon in well water in Washington?

The median radon level across 702 public samples in Washington was 480 pCi/L, with a high of 171,527 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Washington?

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 in Washington

Want the numbers themselves? Download the Washington dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 99,438 samples in Washington. 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 1,023,853 people on private wells in Washington 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: 163,429 well records in Washington, 163,360 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: 42,904 regulated sites located in Washington. 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.