Private wells · by county
Missouri well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Missouri county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
Missouri counties
All 115 counties
- Jefferson CountyWell users 38,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Franklin CountyWell users 37,300Arsenic about 2 in 100Nitrate 0.1 mg/L
- Greene CountyWell users 31,800Arsenic about 2 in 100Nitrate 0.2 mg/L
- Newton CountyWell users 28,300Arsenic about 1 in 100Nitrate 0.2 mg/L
- Camden CountyWell users 21,400Arsenic about 1 in 100Nitrate 0.1 mg/L
- Webster CountyWell users 21,100Arsenic about 1 in 100Nitrate 0.2 mg/L
- Howell CountyWell users 20,300Arsenic about 1 in 100Nitrate 0.3 mg/L
- St. Francois CountyWell users 19,500Arsenic about 2 in 100Nitrate 0.2 mg/L
- Lincoln CountyWell users 19,400Arsenic about 2 in 100Nitrate 0.0 mg/L
- Christian CountyWell users 18,600Arsenic about 1 in 100Nitrate 0.2 mg/L
- Washington CountyWell users 18,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Phelps CountyWell users 17,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Jasper CountyWell users 17,500Arsenic about 1 in 100Nitrate 0.2 mg/L
- Barry CountyWell users 16,800Arsenic about 1 in 100Nitrate 0.2 mg/L
- Polk CountyWell users 16,700Arsenic about 1 in 100Nitrate 0.2 mg/L
- Lawrence CountyWell users 16,400Arsenic about 1 in 100Nitrate 0.2 mg/L
- Stone CountyWell users 16,000Arsenic about 1 in 100Nitrate 0.1 mg/L
- St. Charles CountyWell users 15,600Arsenic about 5 in 100Nitrate 0.0 mg/L
- Miller CountyWell users 14,800Arsenic about 1 in 100Nitrate 0.2 mg/L
- Morgan CountyWell users 13,500Arsenic about 2 in 100Nitrate 0.1 mg/L
- Taney CountyWell users 13,400Arsenic about 1 in 100Nitrate 0.0 mg/L
- Crawford CountyWell users 12,800Arsenic about 1 in 100Nitrate 0.1 mg/L
- Dallas CountyWell users 12,600Arsenic about 1 in 100Nitrate 0.2 mg/L
- Cape Girardeau CountyWell users 12,200Arsenic about 2 in 100Nitrate 0.2 mg/L
- Butler CountyWell users 12,100Arsenic about 3 in 100Nitrate 0.1 mg/L
- McDonald CountyWell users 11,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Texas CountyWell users 11,700Arsenic about 1 in 100Nitrate 0.2 mg/L
- Cole CountyWell users 11,400Arsenic about 2 in 100Nitrate 0.2 mg/L
- Pettis CountyWell users 11,300Arsenic about 3 in 100Nitrate 0.1 mg/L
- Scott CountyWell users 10,800Arsenic about 14 in 100Nitrate 0.4 mg/L
- Wright CountyWell users 10,700Arsenic about 1 in 100Nitrate 0.2 mg/L
- Benton CountyWell users 10,700Arsenic about 1 in 100Nitrate 0.1 mg/L
- Warren CountyWell users 10,500Arsenic about 2 in 100Nitrate 0.0 mg/L
- Douglas CountyWell users 9,700Arsenic about 1 in 100Nitrate 0.2 mg/L
- St. Louis CountyWell users 9,600Arsenic about 2 in 100Nitrate 0.1 mg/L
- Laclede CountyWell users 9,200Arsenic about 1 in 100Nitrate 0.2 mg/L
- Bollinger CountyWell users 9,100Arsenic about 2 in 100Nitrate 0.1 mg/L
- Stoddard CountyWell users 8,700Arsenic about 6 in 100Nitrate 0.1 mg/L
- Dent CountyWell users 8,700Arsenic about 1 in 100Nitrate 0.1 mg/L
- Pulaski CountyWell users 8,500Arsenic about 1 in 100Nitrate 0.1 mg/L
- Ozark CountyWell users 7,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Wayne CountyWell users 7,600Arsenic about 1 in 100Nitrate 0.1 mg/L
- Callaway CountyWell users 7,000Arsenic about 2 in 100Nitrate 0.0 mg/L
- Johnson CountyWell users 7,000Arsenic about 2 in 100Nitrate 0.0 mg/L
- Ste. Genevieve CountyWell users 6,900Arsenic about 4 in 100Nitrate 0.1 mg/L
- Gasconade CountyWell users 6,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Ripley CountyWell users 6,800Arsenic about 1 in 100Nitrate 0.3 mg/L
- Osage CountyWell users 6,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- Maries CountyWell users 6,700Arsenic about 1 in 100Nitrate 0.1 mg/L
- Oregon CountyWell users 6,400Arsenic about 1 in 100Nitrate 0.3 mg/L
- Hickory CountyWell users 6,300Arsenic about 1 in 100Nitrate 0.1 mg/L
- Perry CountyWell users 5,800Arsenic about 2 in 100Nitrate 0.2 mg/L
- St. Clair CountyWell users 5,800Arsenic about 3 in 100Nitrate 0.1 mg/L
- Madison CountyWell users 5,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Henry CountyWell users 5,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- Moniteau CountyWell users 5,500Arsenic about 2 in 100Nitrate 0.3 mg/L
- Iron CountyWell users 5,400Arsenic about 1 in 100Nitrate 0.1 mg/L
- Cedar CountyWell users 5,400Arsenic about 3 in 100Nitrate 0.1 mg/L
- Mississippi CountyWell users 4,900Arsenic about 18 in 100Nitrate 0.5 mg/L
- Montgomery CountyWell users 4,800Arsenic about 4 in 100Nitrate 0.0 mg/L
- Boone CountyWell users 4,700Arsenic about 2 in 100Nitrate 0.0 mg/L
- Cooper CountyWell users 4,600Arsenic about 3 in 100Nitrate 0.2 mg/L
- Reynolds CountyWell users 4,600Arsenic about 1 in 100Nitrate 0.1 mg/L
- Shannon CountyWell users 4,400Arsenic about 1 in 100Nitrate 0.1 mg/L
- Audrain CountyWell users 4,100Arsenic about 3 in 100Nitrate 0.0 mg/L
- Pike CountyWell users 4,100Arsenic about 6 in 100Nitrate 0.1 mg/L
- New Madrid CountyWell users 4,000Arsenic about 7 in 100Nitrate 0.2 mg/L
- Nodaway CountyWell users 3,800Arsenic about 3 in 100Nitrate 2.9 mg/L
- Carter CountyWell users 3,400Arsenic about 1 in 100Nitrate 0.2 mg/L
- Dade CountyWell users 3,300Arsenic about 2 in 100Nitrate 0.1 mg/L
- Clinton CountyWell users 3,200Arsenic about 2 in 100Nitrate 0.8 mg/L
- Dunklin CountyWell users 2,900Arsenic about 8 in 100Nitrate 0.4 mg/L
- Saline CountyWell users 2,700Arsenic about 5 in 100Nitrate 0.1 mg/L
- Vernon CountyWell users 2,600Arsenic about 2 in 100Nitrate 0.1 mg/L
- Marion CountyWell users 2,600Arsenic about 4 in 100Nitrate 0.2 mg/L
- DeKalb CountyWell users 2,500Arsenic about 2 in 100Nitrate 1.4 mg/L
- Ralls CountyWell users 2,500Arsenic about 3 in 100Nitrate 0.1 mg/L
- Jackson CountyWell users 2,500Arsenic about 3 in 100Nitrate 0.4 mg/L
- Ray CountyWell users 2,400Arsenic about 3 in 100Nitrate 0.7 mg/L
- Cass CountyWell users 2,300Arsenic about 1 in 100Nitrate 0.1 mg/L
- Clay CountyWell users 2,300Arsenic about 3 in 100Nitrate 0.2 mg/L
- Caldwell CountyWell users 2,200Arsenic about 2 in 100Nitrate 1.2 mg/L
- Lewis CountyWell users 2,100Arsenic about 2 in 100Nitrate 0.1 mg/L
- Andrew CountyWell users 2,000Arsenic about 5 in 100Nitrate 2.3 mg/L
- Monroe CountyWell users 2,000Arsenic about 3 in 100Nitrate 0.0 mg/L
- Bates CountyWell users 1,900Arsenic about 1 in 100Nitrate 0.3 mg/L
- Clark CountyWell users 1,800Arsenic about 2 in 100Nitrate 0.3 mg/L
- Platte CountyWell users 1,800Arsenic about 3 in 100Nitrate 0.5 mg/L
- Daviess CountyWell users 1,700Arsenic about 3 in 100Nitrate 0.9 mg/L
- Gentry CountyWell users 1,600Arsenic about 3 in 100Nitrate 1.8 mg/L
- Buchanan CountyWell users 1,500Arsenic about 3 in 100Nitrate 1.5 mg/L
- Holt CountyWell users 1,500Arsenic about 9 in 100Nitrate 0.9 mg/L
- Harrison CountyWell users 1,500Arsenic about 2 in 100Nitrate 1.5 mg/L
- Carroll CountyWell users 1,400Arsenic about 3 in 100Nitrate 0.5 mg/L
- Atchison CountyWell users 1,300Arsenic about 8 in 100Nitrate 1.8 mg/L
- Howard CountyWell users 1,200Arsenic about 2 in 100Nitrate 0.1 mg/L
- Schuyler CountyWell users 1,100Arsenic about 2 in 100Nitrate 1.3 mg/L
- Lafayette CountyWell users 1,100Arsenic about 2 in 100Nitrate 0.2 mg/L
- Chariton CountyWell users 1,100Arsenic about 4 in 100Nitrate 0.5 mg/L
- Putnam CountyWell users 1,000Arsenic about 2 in 100Nitrate 1.1 mg/L
- Livingston CountyWell users 960Arsenic about 4 in 100Nitrate 0.3 mg/L
- Randolph CountyWell users 950Arsenic about 1 in 100Nitrate 0.2 mg/L
- Knox CountyWell users 910Arsenic about 2 in 100Nitrate 0.0 mg/L
- Scotland CountyWell users 880Arsenic about 2 in 100Nitrate 1.0 mg/L
- Mercer CountyWell users 850Arsenic about 2 in 100Nitrate 1.0 mg/L
- Macon CountyWell users 840Arsenic about 2 in 100Nitrate 1.4 mg/L
- Shelby CountyWell users 800Arsenic about 3 in 100Nitrate 0.2 mg/L
- Adair CountyWell users 740Arsenic about 2 in 100Nitrate 0.8 mg/L
- Sullivan CountyWell users 600Arsenic about 2 in 100Nitrate 1.3 mg/L
- Worth CountyWell users 570Arsenic about 3 in 100Nitrate 1.8 mg/L
- Linn CountyWell users 480Arsenic about 2 in 100Nitrate 0.7 mg/L
- Pemiscot CountyWell users 460Arsenic about 7 in 100Nitrate 0.2 mg/L
- Grundy CountyWell users 400Arsenic about 4 in 100Nitrate 0.2 mg/L
- Barton CountyWell users 390Arsenic about 3 in 100Nitrate 0.0 mg/L
- St. Louis cityWell users 220Arsenic about 3 in 100Nitrate 0.6 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
What the model can and can’t tell you
- 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.
What to test your well for
- 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
Where to test in Missouri
Use a state-certified lab
Missouri Department of Natural Resources lists the laboratories certified to test drinking water in Missouri.
Commercial · test your own well
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.
Questions
Missouri 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 Missouri?
About 870,600 people across 115 Missouri counties, by the USGS 2010 estimate. USGS models place about 18,800 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 Missouri?
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 Missouri?
Missouri Department of Natural Resources keeps the list of laboratories certified to test drinking water in Missouri. Only use laboratories that are certified to do drinking water testing. (EPA)