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Well water testing in Columbia County, Washington

What official data says about private wells in Columbia County, what to test for, and the state-certified labs nearby.

People on private wells (2015)1,074

About 27% of the county's 3,944 residents. Rank 37 of 39 in Washington.

Arsenic above EPA’s limit (USGS estimate)about 24 people

95% range 19 to 30 private-well users (2010 base year). Rank 32 of 39 in Washington.

EPA radon zone (indoor air)Zone 2

Moderate potential (average indoor radon may be between 2 and 4 pCi/L). EPA says the map should not be used to decide whether an individual home needs testing.

Certified labs in this county0

Labs with an address in this county, from the official state lists on this site, matched by ZIP code.

What to test for in Columbia County

Private wells are not regulated like public water: EPA advises owners to test their well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Your state's own schedule:

  • Coliform bacteria and nitrate every year. If nitrate is 5 mg/L or higher, the state says you may want to re-test in six months. It also suggests testing arsenic at least twice while you own the home, once in summer and once in winter. source

Arsenic. USGS estimates that about 24 people using private wells in Columbia County had arsenic above 10 µg/L, EPA's limit for public water (2010 base year; 95% range 19 to 30). USGS describes this kind of estimate as useful "for broad screening of the population at risk", so it says nothing certain about any one well. Arsenic has no taste or smell: test for it by name.

Radon. EPA puts Columbia County in Zone 2: moderate potential (average indoor radon may be between 2 and 4 pCi/L). That map is about radon in indoor air, and EPA says it should not be used to decide whether an individual home needs testing. If radon is found in your air and you have a well, EPA suggests testing the water too: see radon in well water.

For anything specific to your home (farms nearby, old plumbing, a new baby, a smell or stain), use the which-tests checklist. When the results arrive, check your numbers against EPA's limits.

Estimated private-well users with arsenic above 10 µg/L: Columbia County and Washington's highest countiespeople (2010 base year)
Show the numbers
ItemValueNote
Yakima County6,940 people (2010 base year)
Snohomish County6,178 people (2010 base year)
Benton County5,218 people (2010 base year)
Clark County4,768 people (2010 base year)
Grant County4,097 people (2010 base year)
Columbia County (this county)24 people (2010 base year)

USGS model estimate for broad screening, not a measurement of any well. Only a test tells you about your own well. Source: USGS, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter (Ayotte, Medalie and Qi, 2017), accessed 2026-11-01.

Testing programs and help in Washington

  • Free nitrate and coliform testing for private wells in the Lower Yakima Valley and Western Benton County. source

Buying a home with a well in Columbia County

Loan test (FHA, VA, USDA) in Columbia County, WA

  • VA. Test results are valid for 90 days from the date the local health authority certifies them, unless the local authority says otherwise. VA’s chapter names no list of contaminants: the water must meet the local health authority’s requirements, or EPA guidelines where it has none. Your lender may ask for specific tests.
  • FHA. A well test is required in the situations FHA’s handbook lists, among others, and the report may not be more than 180 days old at disbursement.
  • USDA. Guaranteed loans need a water quality test for a private well, done by the local health authority or a state-certified lab, and no more than 180 days old at closing.

Lenders can ask for more (extra tests, a particular lab, who takes the sample): ask your lender before you book. Federal rules as read on Nov 3, 2026 source 1 source 2 source 3. Full comparison: VA, FHA and USDA well water test requirements. Loan test kits sold by mail, with price and days to results: kits compared.

State-certified labs in Columbia County

None of the labs on our Washington list has an address in Columbia County. Labs elsewhere in the state may take samples by mail or courier: ask the lab, and check the hold time for bacteria before you send one.

Labs on the Washington list whose own websites say they take homeowner samples: Bureau Veritas Canada (2019) Inc. (Mississauga). Use Check my ZIP to sort labs by distance.

See all Washington labs in the finder and filter by the test you need and by labs that take homeowner samples.

Sources and method Private-well population is the USGS 2015 estimate of people on domestic self-supplied water. The arsenic figure is a USGS model estimate on a 2010 population base, not a count of tested wells. Labs are placed in a county by the ZIP code on the state list. These figures come from different USGS products, years and methods, so they can disagree with each other (for example, the arsenic estimate and the well population use different base years). Read them as context for the county, not as facts about any one well. Checked 1 Nov 2026. General information, not medical advice.
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