Oklahoma well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Oklahoma county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 77 counties
- Oklahoma CountyWell users 52,200Arsenic about 3 in 100Nitrate 2.3 mg/L
- Cleveland CountyWell users 33,100Arsenic about 3 in 100Nitrate 1.3 mg/L
- Pottawatomie CountyWell users 25,000Arsenic about 4 in 100Nitrate 1.6 mg/L
- Grady CountyWell users 19,000Arsenic about 3 in 100Nitrate 4.3 mg/L
- Lincoln CountyWell users 18,900Arsenic about 5 in 100Nitrate 1.4 mg/L
- Delaware CountyWell users 18,400Arsenic about 1 in 100Nitrate 0.3 mg/L
- McClain CountyWell users 13,700Arsenic about 3 in 100Nitrate 3.4 mg/L
- Creek CountyWell users 13,300Arsenic about 8 in 100Nitrate 0.4 mg/L
- Logan CountyWell users 12,600Arsenic about 3 in 100Nitrate 2.7 mg/L
- Cherokee CountyWell users 12,500Arsenic about 1 in 100Nitrate 0.3 mg/L
- Canadian CountyWell users 11,600Arsenic about 4 in 100Nitrate 7.3 mg/L
- McCurtain CountyWell users 10,700Arsenic about 2 in 100Nitrate 0.2 mg/L
- Adair CountyWell users 10,400Arsenic about 1 in 100Nitrate 0.4 mg/L
- Caddo CountyWell users 10,000Arsenic about 3 in 100Nitrate 8.5 mg/L
- Payne CountyWell users 9,000Arsenic about 7 in 100Nitrate 2.7 mg/L
- Stephens CountyWell users 8,700Arsenic about 3 in 100Nitrate 3.2 mg/L
- Garfield CountyWell users 8,500Arsenic about 4 in 100Nitrate 10.2 mg/L
- Bryan CountyWell users 8,400Arsenic about 2 in 100Nitrate 0.5 mg/L
- Seminole CountyWell users 7,900Arsenic about 6 in 100Nitrate 0.5 mg/L
- Sequoyah CountyWell users 7,400Arsenic about 2 in 100Nitrate 0.2 mg/L
- Mayes CountyWell users 7,300Arsenic about 2 in 100Nitrate 0.4 mg/L
- Carter CountyWell users 7,200Arsenic about 3 in 100Nitrate 1.2 mg/L
- Le Flore CountyWell users 6,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Comanche CountyWell users 6,000Arsenic about 6 in 100Nitrate 3.2 mg/L
- Choctaw CountyWell users 5,900Arsenic about 2 in 100Nitrate 0.3 mg/L
- Garvin CountyWell users 5,800Arsenic about 3 in 100Nitrate 2.7 mg/L
- Osage CountyWell users 5,800Arsenic about 7 in 100Nitrate 0.8 mg/L
- Ottawa CountyWell users 5,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- Tulsa CountyWell users 4,600Arsenic about 7 in 100Nitrate 1.7 mg/L
- Pontotoc CountyWell users 4,300Arsenic about 6 in 100Nitrate 0.6 mg/L
- Haskell CountyWell users 4,200Arsenic about 4 in 100Nitrate 0.1 mg/L
- Atoka CountyWell users 4,000Arsenic about 2 in 100Nitrate 0.5 mg/L
- Pawnee CountyWell users 4,000Arsenic about 6 in 100Nitrate 0.8 mg/L
- Pushmataha CountyWell users 3,800Arsenic about 2 in 100Nitrate 0.2 mg/L
- Beckham CountyWell users 3,700Arsenic about 4 in 100Nitrate 7.6 mg/L
- Woodward CountyWell users 3,600Arsenic about 3 in 100Nitrate 10.2 mg/L
- Wagoner CountyWell users 3,600Arsenic about 5 in 100Nitrate 1.0 mg/L
- McIntosh CountyWell users 3,500Arsenic about 4 in 100Nitrate 0.3 mg/L
- Muskogee CountyWell users 3,500Arsenic about 4 in 100Nitrate 0.2 mg/L
- Kay CountyWell users 3,400Arsenic about 8 in 100Nitrate 6.6 mg/L
- Custer CountyWell users 3,300Arsenic about 3 in 100Nitrate 6.3 mg/L
- Kingfisher CountyWell users 3,200Arsenic about 6 in 100Nitrate 17.8 mg/L
- Pittsburg CountyWell users 3,200Arsenic about 5 in 100Nitrate 0.2 mg/L
- Rogers CountyWell users 3,000Arsenic about 7 in 100Nitrate 1.1 mg/L
- Major CountyWell users 3,000Arsenic about 4 in 100Nitrate 14.6 mg/L
- Hughes CountyWell users 3,000Arsenic about 6 in 100Nitrate 0.7 mg/L
- Texas CountyWell users 2,900Arsenic about 6 in 100Nitrate 5.5 mg/L
- Beaver CountyWell users 2,700Arsenic about 4 in 100Nitrate 5.2 mg/L
- Okfuskee CountyWell users 2,700Arsenic about 8 in 100Nitrate 1.0 mg/L
- Blaine CountyWell users 2,500Arsenic about 4 in 100Nitrate 12.5 mg/L
- Marshall CountyWell users 2,500Arsenic about 2 in 100Nitrate 0.8 mg/L
- Love CountyWell users 2,500Arsenic about 3 in 100Nitrate 2.7 mg/L
- Johnston CountyWell users 2,400Arsenic about 2 in 100Nitrate 0.6 mg/L
- Washita CountyWell users 2,200Arsenic about 4 in 100Nitrate 10.4 mg/L
- Craig CountyWell users 1,700Arsenic about 3 in 100Nitrate 0.5 mg/L
- Jackson CountyWell users 1,600Arsenic about 3 in 100Nitrate 11.0 mg/L
- Murray CountyWell users 1,600Arsenic about 3 in 100Nitrate 1.0 mg/L
- Okmulgee CountyWell users 1,500Arsenic about 5 in 100Nitrate 0.5 mg/L
- Noble CountyWell users 1,500Arsenic about 4 in 100Nitrate 6.9 mg/L
- Roger Mills CountyWell users 1,400Arsenic about 3 in 100Nitrate 4.2 mg/L
- Dewey CountyWell users 1,300Arsenic about 3 in 100Nitrate 6.5 mg/L
- Ellis CountyWell users 1,300Arsenic about 3 in 100Nitrate 3.2 mg/L
- Harmon CountyWell users 1,200Arsenic about 3 in 100Nitrate 9.4 mg/L
- Alfalfa CountyWell users 910Arsenic about 4 in 100Nitrate 13.3 mg/L
- Jefferson CountyWell users 850Arsenic about 4 in 100Nitrate 6.0 mg/L
- Washington CountyWell users 850Arsenic about 5 in 100Nitrate 1.0 mg/L
- Latimer CountyWell users 810Arsenic about 2 in 100Nitrate 0.1 mg/L
- Woods CountyWell users 800Arsenic about 3 in 100Nitrate 7.7 mg/L
- Cotton CountyWell users 780Arsenic about 7 in 100Nitrate 6.4 mg/L
- Coal CountyWell users 770Arsenic about 5 in 100Nitrate 0.3 mg/L
- Cimarron CountyWell users 710Arsenic about 10 in 100Nitrate 4.2 mg/L
- Nowata CountyWell users 710Arsenic about 4 in 100Nitrate 0.9 mg/L
- Kiowa CountyWell users 680Arsenic about 4 in 100Nitrate 8.2 mg/L
- Tillman CountyWell users 670Arsenic about 4 in 100Nitrate 13.0 mg/L
- Harper CountyWell users 640Arsenic about 3 in 100Nitrate 5.9 mg/L
- Grant CountyWell users 620Arsenic about 6 in 100Nitrate 9.5 mg/L
- Greer CountyWell users 600Arsenic about 3 in 100Nitrate 11.0 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
Oklahoma Department of Environmental Quality lists the laboratories certified to test drinking water in Oklahoma.
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.
Oklahoma 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 Oklahoma?
About 470,000 people across 77 Oklahoma counties, by the USGS 2010 estimate. USGS models place about 17,000 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 Oklahoma?
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 Oklahoma?
Oklahoma Department of Environmental Quality keeps the list of laboratories certified to test drinking water in Oklahoma. Only use laboratories that are certified to do drinking water testing. (EPA)