Private wells
Oregon well water: who's on a well and what to test for
People on private wells
815,900
Homes on wells
19.0%
Est. above arsenic limit
26,100
Every Oregon county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Clackamas County | 97,100 | 22% | 3.5% | 0.2 | 200 ft |
| Marion County | 85,600 | 24% | 5.0% | 0.2 | 142 ft |
| Lane County | 77,000 | 20% | 2.9% | 0.3 | 120 ft |
| Jackson County | 61,900 | 28% | 3.8% | 0.4 | 200 ft |
| Washington County | 54,300 | 8% | 20.7% | 0.1 | 185 ft |
| Josephine County | 52,400 | 60% | 3.1% | 0.3 | 140 ft |
| Linn County | 51,400 | 40% | 3.6% | 0.1 | 100 ft |
| Deschutes County | 37,500 | 20% | 7.0% | 0.2 | 179 ft |
| Douglas County | 33,500 | 31% | 2.6% | 0.1 | 147 ft |
| Yamhill County | 23,500 | 23% | 9.8% | 0.1 | 172 ft |
| Benton County | 23,100 | 24% | 2.8% | 0.1 | 140 ft |
| Umatilla County | 22,300 | 30% | 25.0% | 1.8 | 180 ft |
| Klamath County | 21,600 | 34% | 11.7% | 0.4 | 161 ft |
| Columbia County | 19,100 | 36% | 4.7% | 0.1 | 190 ft |
| Coos County | 19,000 | 29% | 2.6% | 0.1 | 110 ft |
| Polk County | 16,300 | 19% | 3.8% | 0.1 | 140 ft |
| Multnomah County | 15,300 | 2% | 4.6% | 0.2 | 180 ft |
| Crook County | 13,700 | 56% | 7.8% | 0.4 | 305 ft |
| Malheur County | 13,700 | 49% | 23.2% | 1.0 | 98 ft |
| Lincoln County | 8,700 | 13% | 2.0% | 0.1 | 110 ft |
| Curry County | 7,900 | 34% | 1.5% | 0.1 | 104 ft |
| Union County | 7,600 | 29% | 7.7% | 0.4 | 160 ft |
| Jefferson County | 6,700 | 27% | 10.8% | 0.6 | 250 ft |
| Wasco County | 6,300 | 25% | 6.3% | 0.3 | 250 ft |
| Tillamook County | 5,900 | 16% | 1.6% | 0.1 | 119 ft |
| Baker County | 5,400 | 35% | 6.2% | 0.3 | 180 ft |
| Clatsop County | 5,400 | 11% | 1.4% | 0.1 | 78 ft |
| Morrow County | 4,300 | 36% | 25.8% | 1.0 | 162 ft |
| Lake County | 4,000 | 52% | 10.1% | 0.2 | 135 ft |
| Hood River County | 3,400 | 14% | 2.7% | 0.3 | 180 ft |
| Wallowa County | 3,300 | 48% | 4.4% | 0.2 | 125 ft |
| Harney County | 3,200 | 42% | 12.5% | 0.3 | 120 ft |
| Grant County | 3,000 | 43% | 5.5% | 0.1 | 160 ft |
| Wheeler County | 810 | 55% | 6.9% | 0.1 | 154 ft |
| Sherman County | 760 | 39% | 19.0% | 1.4 | 245 ft |
| Gilliam County | 630 | 34% | 19.3% | 0.8 | 250 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Malheur County: about 3,000 people
- Umatilla County: about 2,400 people
- Klamath County: about 2,300 people
- Jackson County: about 2,000 people
- Josephine County: about 1,900 people
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Questions
Which Oregon counties rely most on wells?+
By share of homes: Josephine County (60%), Crook County (56%), Wheeler County (55%), Lake County (52%), Malheur County (49%). By number of people: Clackamas County (97,100), Marion County (85,600), Lane County (77,000).
Is arsenic a problem in Oregon wells?+
USGS estimates about 26,100 Oregon well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Malheur County, Umatilla County, Klamath County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Oregon?+
Yes. The seller must test for arsenic, nitrate and total coliform bacteria after accepting an offer, and send results to the buyer and the Oregon Health Authority (Domestic Well Testing Act, ORS 448.271).
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).