Quick answer
About 522,000 people in Oregon (13.6% of residents) got their water from private wells in 2010, according to USGS estimates. Oregon Health Authority runs the state’s private well guidance. OHA's Domestic Well Safety Program offers a free lab nitrate test to private well users in the Lower Umatilla Basin Groundwater Management Area (northern Morrow and northwestern Umatilla counties) whose well water is used for drinking and cooking.
- People on private wells
- 521,564
- Share of residents
- 13.6%
- Rank among states
- 24th
- Well users modeled above 10 µg/L arsenic
- 6.6%
Where to get your well tested in Oregon
- Oregon Health Authority: Domestic Well Safety Program, the state’s guidance for private well owners.
- Well water testing in Oregon: what to test for and how to collect a sample.
- Certified laboratories in Oregon. Use a lab certified for drinking water, so results are reliable.
Free or low-cost testing
OHA's Domestic Well Safety Program offers a free lab nitrate test to private well users in the Lower Umatilla Basin Groundwater Management Area (northern Morrow and northwestern Umatilla counties) whose well water is used for drinking and cooking. (source)
Mail-in lab kits are another option when no local lab is convenient. See well water test kits for what home kits can and can’t tell you.
What to test for
- Every year: total coliform bacteria and nitrate.
- Before buying equipment: pH, hardness, iron, manganese and, if there’s a smell, hydrogen sulfide.
- Based on location: arsenic, uranium and radon, PFAS, and lead in older plumbing.
USGS modeling estimates that about 6.6% of Oregon’s private well users have water above the 10 µg/L arsenic limit. Arsenic has no taste or smell, so include it in your first test.
Private wells by county
Estimated people relying on private wells in each Oregon county in 2010, the share of residents that represents, and the modeled share of well users with arsenic above 10 µg/L. These are USGS model estimates (2010 population), not measurements of any well. Arsenic is hidden for counties with fewer than 500 well users.
| County | People on wells | Share | Arsenic >10 µg/L |
|---|---|---|---|
| Clackamas County | 56,230 | 15.0% | 3.4% |
| Lane County | 55,466 | 15.8% | 2.9% |
| Marion County | 47,734 | 15.1% | 5.1% |
| Jackson County | 44,741 | 22.0% | 3.9% |
| Linn County | 41,776 | 35.8% | 3.6% |
| Josephine County | 37,956 | 45.9% | 3.0% |
| Washington County | 22,240 | 4.2% | 20.7% |
| Deschutes County | 21,847 | 13.9% | 7.0% |
| Douglas County | 20,664 | 19.2% | 2.7% |
| Umatilla County | 18,806 | 24.8% | 24.9% |
| Klamath County | 18,311 | 27.6% | 11.6% |
| Yamhill County | 16,562 | 16.7% | 9.6% |
Show all 36 counties
| Benton County | 16,170 | 18.9% | 2.7% |
| Malheur County | 13,283 | 42.4% | 23.3% |
| Columbia County | 12,230 | 24.8% | 4.7% |
| Coos County | 10,980 | 17.4% | 2.6% |
| Crook County | 9,726 | 46.4% | 7.8% |
| Multnomah County | 6,834 | 0.9% | 4.5% |
| Union County | 5,886 | 22.9% | 7.7% |
| Polk County | 5,782 | 7.7% | 3.8% |
| Lincoln County | 4,356 | 9.5% | 2.1% |
| Wasco County | 4,098 | 16.3% | 6.2% |
| Lake County | 3,980 | 50.4% | 9.9% |
| Curry County | 3,918 | 17.5% | 1.4% |
| Morrow County | 3,788 | 33.9% | 25.8% |
| Baker County | 3,553 | 22.0% | 6.2% |
| Harney County | 2,582 | 34.8% | 12.7% |
| Wallowa County | 2,380 | 34.0% | 4.3% |
| Tillamook County | 2,256 | 8.9% | 1.4% |
| Jefferson County | 2,049 | 9.4% | 10.9% |
| Clatsop County | 1,691 | 4.6% | 1.6% |
| Grant County | 1,616 | 21.7% | 5.4% |
| Hood River County | 649 | 2.9% | 2.8% |
| Gilliam County | 551 | 29.5% | 19.0% |
| Sherman County | 536 | 30.4% | 19.0% |
| Wheeler County | 337 | 23.4% | – |
Counties with the highest modeled arsenic share: Morrow County (25.8%), Umatilla County (24.9%), Malheur County (23.3%), Washington County (20.7%), Gilliam County (19.0%).
After you get results
Enter your numbers in the test results tool to see what needs treating and in what order. The guide to reading a well water test explains units and limits.
Common questions
Does Oregon offer free well water testing?
OHA's Domestic Well Safety Program offers a free lab nitrate test to private well users in the Lower Umatilla Basin Groundwater Management Area (northern Morrow and northwestern Umatilla counties) whose well water is used for drinking and cooking.
Who oversees private wells in Oregon?
Oregon Health Authority (Domestic Well Safety Program) publishes guidance for private well owners. Private wells aren’t covered by the federal Safe Drinking Water Act, so testing and treatment are up to the owner.
How many people use private wells in Oregon?
USGS estimates about 522,000 people, or 13.6% of the population in 2010. That ranks 24th of the states covered by the estimate.
What should I test my well for in Oregon?
Test every year for total coliform bacteria and nitrate, plus pH, hardness, iron and manganese before buying equipment. Arsenic is a known concern in parts of Oregon, so add it to the first test.
Sources
- Oregon Health Authority: Domestic Well Safety Program
- Oregon Health Authority: well water testing
- Oregon certified laboratories
- Oregon free or low-cost testing
- USGS data release: domestic well locations and populations served, 2000 and 2010 (Johnson, Belitz and Lombard, 2019)
- CDC Environmental Public Health Tracking: private well water data (from USGS)