Well water in Thurston County, Washington

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Testing recommended

tested well samples in Thurston County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.

The strongest signal is E. coli: 7% of 28 local samples were above the limit, too few samples to carry the headline but first on the test list below.

6,174 test results across 13 contaminants from at least 709 wells, 1944 to 2026; nitrate has the most at 1,269. Data refreshed September 15, 2026.

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

An estimated 61,985 people in Thurston County get their drinking water from a private well, per USGS 2015 county water use. That is about 23% of residents.

Separately, the USGS national arsenic model estimates that 3% of the 61,985 people on private wells in Thurston County draw water above 10 ug/L (the model's range is 2% to 4%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Thurston 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
E. coli 1998 to 2022	7%	28	7%	0	1	0 MPN/100mL EPA limit
Nitrate 1944 to 2025	6%	1,269	86%	1.26	47.4	10 mg/L EPA limit
Arsenic 1980 to 2026	5%	303	80%	3.3	21	10 ug/L EPA limit
Copper 1970 to 2017	<1%	155	57%	0.001	1.7	1.3 mg/L EPA limit
Fluoride 1944 to 2017	0%	570	80%	0.1	1.6	4 mg/L EPA limit
Lead 1970 to 2026	0%	178	38%	0	5	15 ug/L EPA limit
Uranium 2002 to 2016	0%	28	43%	0	0.204	30 ug/L EPA limit
Radium (226 + 228) 2004 to 2016	0%	12	25%	0	0.058	5 pCi/L EPA limit
Chloride 1944 to 2024	no limit	1,250	99%	4	7,000	250 mg/L nuisance level
Iron 1944 to 2026	no limit	882	91%	60	1,100,000	300 ug/L nuisance level
Manganese 1962 to 2026	no limit	867	84%	11	12,000	300 ug/L health guideline
Sodium 1944 to 2017	no limit	570	100%	6.3	260	20 mg/L health guideline
Radon 1989 to 1996	no limit	62	95%	400	660	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	<1%537 samples	27%209 samples	3%385 samples	0%138 samples
Fluoride	0%494 samples	0%35 samples	0%41 samples	n/a
Arsenic	2%66 samples	0%32 samples	0%41 samples	8%164 samples
Lead	0%71 samples	0%31 samples	0%41 samples	0%35 samples
Copper	1%83 samples	0%31 samples	0%41 samples	n/a
E. coli	0%12 samples	n/a	n/a	20%10 samples

Arsenic above the limit in Thurston County rose from 0% of 41 samples in the 2010s to 8% of 164 in the 2020s.

Nitrate, fluoride, lead, copper have 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 address

What this means

The contaminants most often above their limit here are e. coli (7% of 28 samples), nitrate (6% of 1,269 samples), and arsenic (5% of 303 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 Thurston County

1
E. coli
7% of 28 local samples were above the limit.
2
Nitrate
6% of 1,269 local samples were above the limit.
3
Arsenic
5% of 303 local samples were above the limit.
4
Copper
<1% of 155 local samples were above the limit.
5
Radon
Median local reading is 400 pCi/L.
6
Chloride
Detected in 99% of local samples.
7
Iron
Detected in 91% of local samples.
8
Volatile organic compounds (VOCs)
26 reported spills and releases on record locally.

Test your Thurston County well for E. coli, nitrate and arsenic

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 Thurston County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

Wells in Thurston County

8,961 domestic wells in Thurston County are on record with the state since 1976. the typical well is 100 feet deep (one in ten goes past 258 feet).

In a typical Thurston County well, the median yield is 30 gallons per minute.

1980s

2,717

1990s

3,973

2000s

1,377

2010s

883

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 Thurston County

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 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 Thurston County

Washington Ecology facility interactions records 26 reported spills and releases in Thurston County, among 1,470 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.

26: reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
1,407: other remediation projects
37: other solid waste facilities

Treatment that fits the local profile

E. coli

Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system

Nitrate

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

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

Copper

Neutralizing filter to raise pH; Point-of-use reverse osmosis

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

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 E. coli

UV disinfection system

whole-house, at the point of entry, about $900

Fix the well cap and casing first; UV keeps bacteria from returning.

For E. coli

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

For nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

For nitrate

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 arsenic

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 copper

Acid neutralizing filter

whole-house, at the point of entry, about $1,200

Raises pH so plumbing stops leaching lead and copper.

Free, no obligation

Get on the list for a free in-home water test in Thurston County

No water treatment company serves Thurston County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Thurston County, and you get an email naming it first.

Common questions

How deep are wells in Thurston County?

The typical domestic well in Thurston County is 100 feet deep, based on 8,961 wells reported to the state since 1976. One in ten is deeper than 258 feet.

Is there arsenic in well water in Thurston County?

Arsenic was detected in 80% of 303 public well samples in Thurston County, and 5% 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 Thurston County?

The median radon level across 62 public samples in Thurston County was 400 pCi/L, with a high of 660 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Thurston 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 Thurston 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: 6,174 samples in Thurston 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 61,985 people on private wells in Thurston 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: 8,964 well records in Thurston County, 8,961 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: 1,470 regulated sites located in Thurston 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.