Well water in Cowlitz County, Washington
In Cowlitz County, 2% of 54 tested well samples exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal.
779 test results across 9 contaminants from at least 118 wells, 1960 to 1997; iron has the most at 148. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 24,480 people in Cowlitz County get their drinking water from a private well, per USGS 2015 county water use. That is about 24% of residents.
Separately, the USGS national arsenic model estimates that 4% of the 24,480 people on private wells in Cowlitz County draw water above 10 ug/L (the model's range is 3% to 6%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Cowlitz 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 |
|---|---|---|---|---|---|---|
| Arsenic 1967 to 1980 | 54 | 98% | 1 | 13 | 10 ug/L EPA limit | |
| Nitrate 1960 to 1980 | 87 | 68% | 0.14 | 11 | 10 mg/L EPA limit | |
| Fluoride 1960 to 1980 | 87 | 100% | 0.1 | 0.4 | 4 mg/L EPA limit | |
| Copper 1967 to 1980 | 70 | 76% | 0 | 0 | 1.3 mg/L EPA limit | |
| Lead 1967 to 1980 | 69 | 81% | 0 | 0 | 15 ug/L EPA limit | |
| Iron 1960 to 1997 | no limit | 148 | 84% | 145 | 75,000 | 300 ug/L nuisance level |
| Chloride 1960 to 1997 | no limit | 93 | 100% | 5.1 | 83 | 250 mg/L nuisance level |
| Sodium 1960 to 1997 | no limit | 91 | 100% | 8.7 | 92 | 20 mg/L health guideline |
| Manganese 1962 to 1980 | no limit | 80 | 89% | 110 | 4,600 | 300 ug/L health guideline |
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 arsenic (2% of 54 samples) and nitrate (1% of 87 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.
Iron, Chloride, 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 Cowlitz County
- 1Arsenic2% of 54 local samples were above the limit.
- 2Nitrate1% of 87 local samples were above the limit.
- 3Coliform bacteriaRecommended for every private well, every year.
- 4FluorideDetected in 100% of local samples.
- 5ChlorideDetected in 100% of local samples.
- 6ManganeseDetected in 89% of local samples.
- 7IronDetected in 84% of local samples.
- 8Volatile organic compounds (VOCs)50 reported spills and releases on record locally.
Test your Cowlitz County well for arsenic, nitrate and coliform bacteria
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 Cowlitz County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Cowlitz County
5,785 domestic wells in Cowlitz County are on record with the state since 1991. the typical well is 201 feet deep (one in ten goes past 482 feet).
In a typical Cowlitz County well, the median yield is 20 gallons per minute.
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 Cowlitz 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 Cowlitz County
Washington Ecology facility interactions records 50 reported spills and releases in Cowlitz County, among 865 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.
- 50
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 783
- other remediation projects
- 32
- other solid waste facilities
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
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 arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
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 arsenic
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 iron
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 Cowlitz County
No water treatment company serves Cowlitz 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 Cowlitz County, and you get an email naming it first.
Common questions
How deep are wells in Cowlitz County?
The typical domestic well in Cowlitz County is 201 feet deep, based on 5,785 wells reported to the state since 1991. One in ten is deeper than 482 feet.
Is there arsenic in well water in Cowlitz County?
Arsenic was detected in 98% of 54 public well samples in Cowlitz County, and 2% 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 Cowlitz 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 Cowlitz 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: 779 samples in Cowlitz 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 24,480 people on private wells in Cowlitz 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: 5,788 well records in Cowlitz County, 5,785 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: 865 regulated sites located in Cowlitz 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.