Ohio well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Ohio county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 88 counties
- Stark CountyWell users 100,600Arsenic about 7 in 100Nitrate 0.2 mg/L
- Summit CountyWell users 87,200Arsenic about 6 in 100Nitrate 0.2 mg/L
- Trumbull CountyWell users 57,700Arsenic about 25 in 100Nitrate 0.0 mg/L
- Geauga CountyWell users 56,600Arsenic about 8 in 100Nitrate 0.0 mg/L
- Portage CountyWell users 52,300Arsenic about 11 in 100Nitrate 0.1 mg/L
- Licking CountyWell users 50,800Arsenic about 14 in 100Nitrate 0.0 mg/L
- Wayne CountyWell users 47,300Arsenic about 10 in 100Nitrate 0.1 mg/L
- Columbiana CountyWell users 42,900Arsenic about 5 in 100Nitrate 0.1 mg/L
- Richland CountyWell users 41,700Arsenic about 19 in 100Nitrate 0.0 mg/L
- Fairfield CountyWell users 40,500Arsenic about 13 in 100Nitrate 0.1 mg/L
- Clark CountyWell users 38,000Arsenic about 15 in 100Nitrate 0.2 mg/L
- Franklin CountyWell users 33,400Arsenic about 9 in 100Nitrate 0.1 mg/L
- Ashtabula CountyWell users 33,100Arsenic about 29 in 100Nitrate 0.0 mg/L
- Mahoning CountyWell users 31,300Arsenic about 10 in 100Nitrate 0.1 mg/L
- Allen CountyWell users 30,100Arsenic about 10 in 100Nitrate 0.0 mg/L
- Montgomery CountyWell users 29,500Arsenic about 18 in 100Nitrate 0.1 mg/L
- Wood CountyWell users 29,400Arsenic about 4 in 100Nitrate 0.0 mg/L
- Miami CountyWell users 28,100Arsenic about 27 in 100Nitrate 0.1 mg/L
- Greene CountyWell users 27,500Arsenic about 17 in 100Nitrate 0.2 mg/L
- Darke CountyWell users 27,000Arsenic about 57 in 100Nitrate 0.0 mg/L
- Tuscarawas CountyWell users 26,100Arsenic about 3 in 100Nitrate 0.1 mg/L
- Holmes CountyWell users 25,600Arsenic about 3 in 100Nitrate 0.1 mg/L
- Knox CountyWell users 25,500Arsenic about 7 in 100Nitrate 0.1 mg/L
- Morrow CountyWell users 24,800Arsenic about 16 in 100Nitrate 0.0 mg/L
- Lucas CountyWell users 24,500Arsenic about 5 in 100Nitrate 0.0 mg/L
- Pickaway CountyWell users 23,200Arsenic about 10 in 100Nitrate 0.2 mg/L
- Sandusky CountyWell users 22,500Arsenic about 12 in 100Nitrate 0.0 mg/L
- Seneca CountyWell users 21,900Arsenic about 11 in 100Nitrate 0.0 mg/L
- Medina CountyWell users 21,900Arsenic about 15 in 100Nitrate 0.0 mg/L
- Muskingum CountyWell users 21,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Union CountyWell users 21,700Arsenic about 3 in 100Nitrate 0.0 mg/L
- Logan CountyWell users 21,400Arsenic about 13 in 100Nitrate 0.0 mg/L
- Shelby CountyWell users 19,400Arsenic about 36 in 100Nitrate 0.0 mg/L
- Champaign CountyWell users 19,300Arsenic about 17 in 100Nitrate 0.1 mg/L
- Ross CountyWell users 19,200Arsenic about 4 in 100Nitrate 0.3 mg/L
- Marion CountyWell users 19,000Arsenic about 4 in 100Nitrate 0.0 mg/L
- Hancock CountyWell users 19,000Arsenic about 5 in 100Nitrate 0.0 mg/L
- Butler CountyWell users 18,800Arsenic about 6 in 100Nitrate 0.9 mg/L
- Putnam CountyWell users 17,600Arsenic about 2 in 100Nitrate 0.0 mg/L
- Ashland CountyWell users 17,500Arsenic about 14 in 100Nitrate 0.1 mg/L
- Madison CountyWell users 17,500Arsenic about 7 in 100Nitrate 0.0 mg/L
- Preble CountyWell users 17,300Arsenic about 21 in 100Nitrate 0.1 mg/L
- Fulton CountyWell users 16,500Arsenic about 17 in 100Nitrate 0.0 mg/L
- Auglaize CountyWell users 16,400Arsenic about 8 in 100Nitrate 0.0 mg/L
- Mercer CountyWell users 16,400Arsenic about 12 in 100Nitrate 0.0 mg/L
- Carroll CountyWell users 16,000Arsenic about 3 in 100Nitrate 0.2 mg/L
- Williams CountyWell users 15,700Arsenic about 15 in 100Nitrate 0.0 mg/L
- Huron CountyWell users 15,700Arsenic about 15 in 100Nitrate 0.0 mg/L
- Coshocton CountyWell users 15,600Arsenic about 2 in 100Nitrate 0.1 mg/L
- Warren CountyWell users 15,400Arsenic about 9 in 100Nitrate 0.8 mg/L
- Hocking CountyWell users 14,700Arsenic about 3 in 100Nitrate 0.0 mg/L
- Ottawa CountyWell users 14,600Arsenic about 12 in 100Nitrate 0.0 mg/L
- Jefferson CountyWell users 14,000Arsenic about 3 in 100Nitrate 0.2 mg/L
- Delaware CountyWell users 13,600Arsenic about 10 in 100Nitrate 0.0 mg/L
- Perry CountyWell users 13,600Arsenic about 4 in 100Nitrate 0.2 mg/L
- Lake CountyWell users 13,500Arsenic about 11 in 100Nitrate 0.3 mg/L
- Crawford CountyWell users 12,800Arsenic about 22 in 100Nitrate 0.0 mg/L
- Hardin CountyWell users 12,700Arsenic about 3 in 100Nitrate 0.0 mg/L
- Washington CountyWell users 12,100Arsenic about 2 in 100Nitrate 0.2 mg/L
- Cuyahoga CountyWell users 12,100Arsenic about 7 in 100Nitrate 0.0 mg/L
- Van Wert CountyWell users 11,600Arsenic about 3 in 100Nitrate 0.0 mg/L
- Lawrence CountyWell users 11,400Arsenic about 3 in 100Nitrate 0.2 mg/L
- Defiance CountyWell users 11,300Arsenic about 2 in 100Nitrate 0.0 mg/L
- Henry CountyWell users 11,100Arsenic about 2 in 100Nitrate 0.0 mg/L
- Paulding CountyWell users 10,900Arsenic about 2 in 100Nitrate 0.0 mg/L
- Clinton CountyWell users 10,800Arsenic about 22 in 100Nitrate 0.0 mg/L
- Highland CountyWell users 10,500Arsenic about 15 in 100Nitrate 0.3 mg/L
- Fayette CountyWell users 10,500Arsenic about 19 in 100Nitrate 0.0 mg/L
- Guernsey CountyWell users 10,200Arsenic about 2 in 100Nitrate 0.1 mg/L
- Wyandot CountyWell users 9,600Arsenic about 6 in 100Nitrate 0.0 mg/L
- Erie CountyWell users 8,300Arsenic about 9 in 100Nitrate 0.0 mg/L
- Belmont CountyWell users 8,200Arsenic about 2 in 100Nitrate 0.3 mg/L
- Vinton CountyWell users 7,600Arsenic about 3 in 100Nitrate 0.0 mg/L
- Lorain CountyWell users 7,400Arsenic about 10 in 100Nitrate 0.0 mg/L
- Pike CountyWell users 7,000Arsenic about 2 in 100Nitrate 0.2 mg/L
- Jackson CountyWell users 6,600Arsenic about 2 in 100Nitrate 0.1 mg/L
- Hamilton CountyWell users 6,100Arsenic about 5 in 100Nitrate 0.7 mg/L
- Morgan CountyWell users 5,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Athens CountyWell users 5,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Harrison CountyWell users 5,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- Scioto CountyWell users 5,400Arsenic about 3 in 100Nitrate 0.2 mg/L
- Meigs CountyWell users 5,000Arsenic about 3 in 100Nitrate 0.1 mg/L
- Adams CountyWell users 5,000Arsenic about 4 in 100Nitrate 0.4 mg/L
- Monroe CountyWell users 4,600Arsenic about 3 in 100Nitrate 0.1 mg/L
- Clermont CountyWell users 3,700Arsenic about 7 in 100Nitrate 0.2 mg/L
- Gallia CountyWell users 3,700Arsenic about 3 in 100Nitrate 0.2 mg/L
- Noble CountyWell users 3,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Brown CountyWell users 2,900Arsenic about 8 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
Ohio Environmental Protection Agency lists the laboratories certified to test drinking water in Ohio.
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.
Ohio 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 Ohio?
About 1.8 million people across 88 Ohio counties, by the USGS 2010 estimate. USGS models place about 202,700 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 Ohio?
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 Ohio?
Ohio Environmental Protection Agency keeps the list of laboratories certified to test drinking water in Ohio. Only use laboratories that are certified to do drinking water testing. (EPA)