Well water in Clark County, Washington

In Clark County, 5% of 154 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.

4,101 test results across 12 contaminants from at least 225 wells, 1949 to 2012; sodium has the most at 719. Data refreshed September 15, 2026.

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

An estimated 82,175 people in Clark County get their drinking water from a private well, per USGS 2015 county water use. That is about 18% of residents.

Separately, the USGS national arsenic model estimates that 6% of the 82,175 people on private wells in Clark County draw water above 10 ug/L (the model's range is 4% to 8%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Clark 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
Nitrate 1949 to 2012	5%	154	75%	0.315	16.1	10 mg/L EPA limit
Lead 1971 to 2005	<1%	663	95%	0.71	42	15 ug/L EPA limit
Copper 1971 to 2003	<1%	658	98%	0.003	2.02	1.3 mg/L EPA limit
Arsenic 1980 to 2003	0%	649	98%	1	5.95	10 ug/L EPA limit
Fluoride 1949 to 1988	0%	125	100%	0.2	2	4 mg/L EPA limit
Radium (226 + 228) 1988	0%	44	27%	0	1	5 pCi/L EPA limit
Uranium 1988	0%	22	9%	0	1	30 ug/L EPA limit
Sodium 1949 to 2005	no limit	719	100%	8.28	154	20 mg/L health guideline
Manganese 1962 to 2005	no limit	705	94%	5	7,080	300 ug/L health guideline
Chloride 1949 to 2005	no limit	154	100%	3.4	110	250 mg/L nuisance level
Iron 1949 to 1988	no limit	126	70%	11	7,700	300 ug/L nuisance level
Radon 1988	no limit	82	90%	320	820	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
Lead	<1%608 samples	0%55 samples	n/a	n/a
Copper	<1%608 samples	2%50 samples	n/a	n/a
Arsenic	0%599 samples	0%50 samples	n/a	n/a
Nitrate	2%124 samples	n/a	23%22 samples	n/a

Nitrate above the limit in Clark County rose from 2% of 124 samples before 2000 to 23% of 22 in the 2010s.

Lead, copper, arsenic 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 nitrate (5% of 154 samples), lead (<1% of 663 samples), and copper (<1% of 658 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.

Manganese, Chloride, and Iron 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 Clark County

1
Nitrate
5% of 154 local samples were above the limit.
2
Lead
<1% of 663 local samples were above the limit.
3
Copper
<1% of 658 local samples were above the limit.
4
Coliform bacteria
Recommended for every private well, every year.
5
Radon
Median local reading is 320 pCi/L.
6
Fluoride
Detected in 100% of local samples.
7
Chloride
Detected in 100% of local samples.
8
Volatile organic compounds (VOCs)
60 reported spills and releases on record locally.

Test your Clark County well for nitrate, lead and copper

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

Wells in Clark County

7,037 domestic wells in Clark County are on record with the state since 1976. the typical well is 183 feet deep (one in ten goes past 445 feet).

In a typical Clark County well, the median yield is 20 gallons per minute.

2,362

1990s

2,430

2000s

1,381

2010s

858

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 Clark 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 Clark County

Washington Ecology facility interactions records 60 reported spills and releases in Clark County, among 1,654 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.

60: reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
1,552: other remediation projects
42: other solid waste facilities

Treatment that fits the local profile

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

Copper

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

Manganese

Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); 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 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 lead

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 lead

Acid neutralizing filter

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

Raises pH so plumbing stops leaching lead and copper.

For manganese

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

Free, no obligation

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

No water treatment company serves Clark 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 Clark County, and you get an email naming it first.

Common questions

How deep are wells in Clark County?

The typical domestic well in Clark County is 183 feet deep, based on 7,037 wells reported to the state since 1976. One in ten is deeper than 445 feet.

Is there arsenic in well water in Clark County?

Arsenic was detected in 98% of 649 public well samples in Clark County, and 0% 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 Clark County?

The median radon level across 82 public samples in Clark County was 320 pCi/L, with a high of 820 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Clark 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 Clark 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: 4,101 samples in Clark 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 82,175 people on private wells in Clark 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: 7,037 well records in Clark County, 7,037 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: 1,654 regulated sites located in Clark 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.