Oregon well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Oregon county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 36 counties
- Clackamas CountyWell users 56,200Arsenic about 4 in 100Nitrate 0.2 mg/L
- Lane CountyWell users 55,500Arsenic about 3 in 100Nitrate 0.3 mg/L
- Marion CountyWell users 47,700Arsenic about 5 in 100Nitrate 0.2 mg/L
- Jackson CountyWell users 44,700Arsenic about 4 in 100Nitrate 0.4 mg/L
- Linn CountyWell users 41,800Arsenic about 4 in 100Nitrate 0.1 mg/L
- Josephine CountyWell users 38,000Arsenic about 3 in 100Nitrate 0.3 mg/L
- Washington CountyWell users 22,200Arsenic about 21 in 100Nitrate 0.1 mg/L
- Deschutes CountyWell users 21,800Arsenic about 7 in 100Nitrate 0.2 mg/L
- Douglas CountyWell users 20,700Arsenic about 3 in 100Nitrate 0.1 mg/L
- Umatilla CountyWell users 18,800Arsenic about 25 in 100Nitrate 1.8 mg/L
- Klamath CountyWell users 18,300Arsenic about 12 in 100Nitrate 0.4 mg/L
- Yamhill CountyWell users 16,600Arsenic about 10 in 100Nitrate 0.1 mg/L
- Benton CountyWell users 16,200Arsenic about 3 in 100Nitrate 0.1 mg/L
- Malheur CountyWell users 13,300Arsenic about 23 in 100Nitrate 1.0 mg/L
- Columbia CountyWell users 12,200Arsenic about 5 in 100Nitrate 0.1 mg/L
- Coos CountyWell users 11,000Arsenic about 3 in 100Nitrate 0.1 mg/L
- Crook CountyWell users 9,700Arsenic about 8 in 100Nitrate 0.4 mg/L
- Multnomah CountyWell users 6,800Arsenic about 5 in 100Nitrate 0.2 mg/L
- Union CountyWell users 5,900Arsenic about 8 in 100Nitrate 0.4 mg/L
- Polk CountyWell users 5,800Arsenic about 4 in 100Nitrate 0.1 mg/L
- Lincoln CountyWell users 4,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Wasco CountyWell users 4,100Arsenic about 6 in 100Nitrate 0.3 mg/L
- Lake CountyWell users 4,000Arsenic about 10 in 100Nitrate 0.2 mg/L
- Curry CountyWell users 3,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Morrow CountyWell users 3,800Arsenic about 26 in 100Nitrate 1.0 mg/L
- Baker CountyWell users 3,600Arsenic about 6 in 100Nitrate 0.3 mg/L
- Harney CountyWell users 2,600Arsenic about 12 in 100Nitrate 0.3 mg/L
- Wallowa CountyWell users 2,400Arsenic about 4 in 100Nitrate 0.2 mg/L
- Tillamook CountyWell users 2,300Arsenic about 2 in 100Nitrate 0.0 mg/L
- Jefferson CountyWell users 2,000Arsenic about 11 in 100Nitrate 0.6 mg/L
- Clatsop CountyWell users 1,700Arsenic about 1 in 100Nitrate 0.1 mg/L
- Grant CountyWell users 1,600Arsenic about 6 in 100Nitrate 0.1 mg/L
- Hood River CountyWell users 650Arsenic about 3 in 100Nitrate 0.3 mg/L
- Gilliam CountyWell users 550Arsenic about 19 in 100Nitrate 0.8 mg/L
- Sherman CountyWell users 540Arsenic about 19 in 100Nitrate 1.4 mg/L
- Wheeler CountyWell users 340Arsenic about 7 in 100Nitrate 0.1 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Oregon Health Authority lists the laboratories certified to test drinking water in Oregon.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
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Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Oregon well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Oregon?
About 521,600 people across 36 Oregon counties, by the USGS 2010 estimate. USGS models place about 34,700 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Oregon?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Oregon?
Oregon Health Authority keeps the list of laboratories certified to test drinking water in Oregon. Only use laboratories that are certified to do drinking water testing. (EPA)