South Dakota well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every South Dakota county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 66 counties
- Pennington CountyWell users 11,400Arsenic about 3 in 100Nitrate 0.8 mg/L
- Minnehaha CountyWell users 9,200Arsenic about 5 in 100Nitrate 1.1 mg/L
- Meade CountyWell users 8,300Arsenic about 3 in 100Nitrate 0.7 mg/L
- Lawrence CountyWell users 7,200Arsenic about 2 in 100Nitrate 0.4 mg/L
- Oglala Lakota CountyWell users 5,700Arsenic about 4 in 100Nitrate 1.2 mg/L
- Custer CountyWell users 4,800Arsenic about 3 in 100Nitrate 0.8 mg/L
- Beadle CountyWell users 4,600Arsenic about 3 in 100Nitrate 0.0 mg/L
- Roberts CountyWell users 4,100Arsenic about 6 in 100Nitrate 0.3 mg/L
- Brown CountyWell users 3,400Arsenic about 10 in 100Nitrate 0.1 mg/L
- Codington CountyWell users 3,300Arsenic about 5 in 100Nitrate 0.7 mg/L
- Todd CountyWell users 3,100Arsenic about 3 in 100Nitrate 2.0 mg/L
- Brookings CountyWell users 3,000Arsenic about 4 in 100Nitrate 0.8 mg/L
- Union CountyWell users 3,000Arsenic about 5 in 100Nitrate 1.2 mg/L
- Spink CountyWell users 2,200Arsenic about 6 in 100Nitrate 0.0 mg/L
- Fall River CountyWell users 1,900Arsenic about 5 in 100Nitrate 0.7 mg/L
- Corson CountyWell users 1,800Arsenic about 5 in 100Nitrate 0.3 mg/L
- Bennett CountyWell users 1,700Arsenic about 4 in 100Nitrate 1.3 mg/L
- Butte CountyWell users 1,700Arsenic about 3 in 100Nitrate 0.3 mg/L
- Davison CountyWell users 1,700Arsenic about 2 in 100Nitrate 0.7 mg/L
- Lincoln CountyWell users 1,600Arsenic about 7 in 100Nitrate 0.7 mg/L
- Marshall CountyWell users 1,500Arsenic about 8 in 100Nitrate 0.2 mg/L
- Perkins CountyWell users 1,500Arsenic about 4 in 100Nitrate 0.2 mg/L
- Turner CountyWell users 1,500Arsenic about 5 in 100Nitrate 0.6 mg/L
- Sanborn CountyWell users 1,400Arsenic about 3 in 100Nitrate 0.0 mg/L
- Grant CountyWell users 1,400Arsenic about 7 in 100Nitrate 0.4 mg/L
- Hand CountyWell users 1,400Arsenic about 5 in 100Nitrate 0.3 mg/L
- Jackson CountyWell users 1,400Arsenic about 3 in 100Nitrate 1.1 mg/L
- Hughes CountyWell users 1,300Arsenic about 3 in 100Nitrate 0.2 mg/L
- Lake CountyWell users 1,300Arsenic about 4 in 100Nitrate 0.3 mg/L
- Day CountyWell users 1,100Arsenic about 3 in 100Nitrate 0.2 mg/L
- McCook CountyWell users 1,000Arsenic about 4 in 100Nitrate 0.1 mg/L
- Yankton CountyWell users 990Arsenic about 4 in 100Nitrate 0.2 mg/L
- Hutchinson CountyWell users 940Arsenic about 4 in 100Nitrate 0.2 mg/L
- Hamlin CountyWell users 920Arsenic about 5 in 100Nitrate 0.7 mg/L
- Moody CountyWell users 910Arsenic about 5 in 100Nitrate 1.4 mg/L
- Gregory CountyWell users 880Arsenic about 2 in 100Nitrate 2.3 mg/L
- Tripp CountyWell users 870Arsenic about 2 in 100Nitrate 1.9 mg/L
- Aurora CountyWell users 860Arsenic about 3 in 100Nitrate 0.2 mg/L
- Douglas CountyWell users 850Arsenic about 3 in 100Nitrate 0.1 mg/L
- Lyman CountyWell users 850Arsenic about 3 in 100Nitrate 0.0 mg/L
- Harding CountyWell users 830Arsenic about 5 in 100Nitrate 0.3 mg/L
- Charles Mix CountyWell users 820Arsenic about 2 in 100Nitrate 0.1 mg/L
- McPherson CountyWell users 810Arsenic about 7 in 100Nitrate 0.2 mg/L
- Faulk CountyWell users 780Arsenic about 5 in 100Nitrate 0.0 mg/L
- Miner CountyWell users 770Arsenic about 3 in 100Nitrate 0.0 mg/L
- Jerauld CountyWell users 760Arsenic about 4 in 100Nitrate 0.5 mg/L
- Deuel CountyWell users 750Arsenic about 6 in 100Nitrate 0.6 mg/L
- Dewey CountyWell users 730Arsenic about 3 in 100Nitrate 0.2 mg/L
- Clark CountyWell users 720Arsenic about 3 in 100Nitrate 0.1 mg/L
- Kingsbury CountyWell users 720Arsenic about 4 in 100Nitrate 0.1 mg/L
- Edmunds CountyWell users 710Arsenic about 5 in 100Nitrate 0.0 mg/L
- Mellette CountyWell users 710Arsenic about 3 in 100Nitrate 1.2 mg/L
- Clay CountyWell users 700Arsenic about 4 in 100Nitrate 0.6 mg/L
- Bon Homme CountyWell users 610Arsenic about 3 in 100Nitrate 0.1 mg/L
- Haakon CountyWell users 590Arsenic about 3 in 100Nitrate 0.3 mg/L
- Sully CountyWell users 570Arsenic about 4 in 100Nitrate 0.4 mg/L
- Ziebach CountyWell users 570Arsenic about 4 in 100Nitrate 0.3 mg/L
- Potter CountyWell users 480Arsenic about 4 in 100Nitrate 0.4 mg/L
- Campbell CountyWell users 480Arsenic about 5 in 100Nitrate 0.5 mg/L
- Hyde CountyWell users 470Arsenic about 4 in 100Nitrate 0.5 mg/L
- Hanson CountyWell users 470Arsenic about 3 in 100Nitrate 0.4 mg/L
- Stanley CountyWell users 420Arsenic about 3 in 100Nitrate 0.0 mg/L
- Buffalo CountyWell users 370Arsenic about 4 in 100Nitrate 0.1 mg/L
- Walworth CountyWell users 320Arsenic about 4 in 100Nitrate 0.5 mg/L
- Jones CountyWell users 140Arsenic about 3 in 100Nitrate 0.1 mg/L
- Brule CountyWell users 140Arsenic about 3 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
South Dakota Department of Agriculture & Natural Resources lists the laboratories certified to test drinking water in South Dakota.
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.
South Dakota 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 South Dakota?
About 122,200 people across 66 South Dakota counties, by the USGS 2010 estimate. USGS models place about 5,000 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 South Dakota?
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 South Dakota?
South Dakota Department of Agriculture & Natural Resources keeps the list of laboratories certified to test drinking water in South Dakota. Only use laboratories that are certified to do drinking water testing. (EPA)