Private wells
Ohio well water: who's on a well and what to test for
People on private wells
2,333,800
Homes on wells
18.5%
Est. above arsenic limit
189,200
Every Ohio county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Stark County | 122,800 | 31% | 6.7% | 0.2 | 114 ft |
| Summit County | 115,000 | 20% | 5.6% | 0.2 | 80 ft |
| Geauga County | 77,000 | 79% | 8.2% | 0.0 | 102 ft |
| Portage County | 71,700 | 44% | 11.0% | 0.1 | 92 ft |
| Licking County | 65,700 | 36% | 13.7% | 0.0 | 136 ft |
| Trumbull County | 62,300 | 29% | 25.3% | 0.0 | 92 ft |
| Wayne County | 58,800 | 46% | 9.7% | 0.1 | 107 ft |
| Fairfield County | 54,000 | 33% | 13.2% | 0.1 | 100 ft |
| Franklin County | 52,100 | 4% | 9.3% | 0.1 | 88 ft |
| Columbiana County | 51,200 | 47% | 4.9% | 0.1 | 128 ft |
| Richland County | 46,800 | 35% | 19.5% | 0.0 | 123 ft |
| Clark County | 44,200 | 31% | 14.6% | 0.2 | 84 ft |
| Medina County | 43,600 | 23% | 15.2% | 0.0 | 90 ft |
| Mahoning County | 41,000 | 17% | 10.5% | 0.1 | 114 ft |
| Ashtabula County | 34,900 | 32% | 28.8% | 0.1 | 59 ft |
| Montgomery County | 34,700 | 6% | 18.3% | 0.1 | 75 ft |
| Greene County | 34,700 | 19% | 17.0% | 0.2 | 91 ft |
| Knox County | 34,000 | 50% | 7.4% | 0.1 | 140 ft |
| Miami County | 34,000 | 30% | 27.0% | 0.1 | 82 ft |
| Allen County | 32,500 | 30% | 10.3% | 0.0 | 69 ft |
| Holmes County | 31,600 | 67% | 3.4% | 0.1 | 145 ft |
| Tuscarawas County | 31,500 | 32% | 2.7% | 0.1 | 125 ft |
| Muskingum County | 29,300 | 32% | 1.8% | 0.1 | 100 ft |
| Wood County | 29,200 | 21% | 4.3% | 0.0 | 80 ft |
| Butler County | 28,700 | 7% | 6.0% | 0.9 | 60 ft |
| Lucas County | 28,600 | 6% | 4.6% | 0.0 | 79 ft |
| Warren County | 28,400 | 12% | 9.2% | 0.8 | 60 ft |
| Darke County | 27,700 | 49% | 56.8% | 0.0 | 101 ft |
| Ross County | 26,800 | 35% | 4.2% | 0.3 | 75 ft |
| Union County | 25,400 | 38% | 3.3% | 0.0 | 98 ft |
| Morrow County | 24,100 | 67% | 16.0% | 0.0 | 81 ft |
| Sandusky County | 24,000 | 39% | 12.3% | 0.0 | 90 ft |
| Seneca County | 23,600 | 41% | 10.9% | 0.0 | 90 ft |
| Pickaway County | 23,300 | 42% | 10.0% | 0.2 | 90 ft |
| Ashland County | 22,900 | 41% | 13.6% | 0.1 | 101 ft |
| Delaware County | 22,700 | 10% | 9.5% | 0.0 | 72 ft |
| Logan County | 21,300 | 48% | 13.2% | 0.0 | 112 ft |
| Shelby County | 21,000 | 40% | 35.9% | 0.0 | 109 ft |
| Clermont County | 20,800 | 10% | 6.6% | 0.2 | 70 ft |
| Lake County | 20,400 | 8% | 11.0% | 0.3 | 76 ft |
| Washington County | 20,300 | 33% | 2.3% | 0.2 | 80 ft |
| Preble County | 19,800 | 46% | 21.0% | 0.1 | 77 ft |
| Champaign County | 19,800 | 47% | 16.8% | 0.1 | 92 ft |
| Marion County | 19,700 | 29% | 3.6% | 0.0 | 76 ft |
| Lorain County | 19,300 | 5% | 9.9% | 0.0 | 56 ft |
| Fulton County | 18,800 | 43% | 16.5% | 0.0 | 103 ft |
| Scioto County | 18,700 | 25% | 2.8% | 0.1 | 54 ft |
| Huron County | 18,600 | 30% | 15.1% | 0.0 | 62 ft |
| Highland County | 18,600 | 40% | 15.5% | 0.3 | 100 ft |
| Mercer County | 18,400 | 42% | 12.2% | 0.0 | 142 ft |
| Coshocton County | 18,400 | 48% | 2.2% | 0.1 | 96 ft |
| Carroll County | 18,100 | 67% | 2.9% | 0.2 | 136 ft |
| Ottawa County | 18,000 | 41% | 11.5% | 0.0 | 75 ft |
| Putnam County | 17,900 | 50% | 2.0% | 0.0 | 73 ft |
| Perry County | 17,600 | 48% | 3.8% | 0.2 | 115 ft |
| Hancock County | 17,500 | 21% | 4.6% | 0.0 | 65 ft |
| Brown County | 17,000 | 37% | 8.2% | 0.1 | 86 ft |
| Hocking County | 16,800 | 60% | 2.8% | 0.0 | 200 ft |
| Lawrence County | 16,800 | 28% | 3.3% | 0.2 | 80 ft |
| Jefferson County | 16,600 | 25% | 2.8% | 0.2 | 114 ft |
| Cuyahoga County | 15,900 | 1% | 6.6% | 0.0 | 65 ft |
| Madison County | 15,900 | 38% | 7.4% | 0.0 | 102 ft |
| Auglaize County | 15,700 | 33% | 8.3% | 0.0 | 106 ft |
| Williams County | 15,500 | 40% | 15.0% | 0.0 | 99 ft |
| Adams County | 15,300 | 54% | 4.0% | 0.4 | 70 ft |
| Belmont County | 15,200 | 22% | 2.3% | 0.3 | 90 ft |
| Athens County | 14,700 | 26% | 2.5% | 0.1 | 75 ft |
| Clinton County | 14,500 | 33% | 21.7% | 0.1 | 90 ft |
| Guernsey County | 14,300 | 36% | 1.5% | 0.1 | 105 ft |
| Defiance County | 13,900 | 34% | 2.5% | 0.0 | 88 ft |
| Erie County | 13,400 | 16% | 8.6% | 0.0 | 62 ft |
| Pike County | 13,400 | 46% | 2.1% | 0.2 | 65 ft |
| Crawford County | 13,200 | 29% | 22.1% | 0.0 | 60 ft |
| Hardin County | 13,100 | 40% | 3.2% | 0.0 | 87 ft |
| Gallia County | 12,600 | 42% | 2.8% | 0.2 | 70 ft |
| Jackson County | 12,600 | 36% | 2.5% | 0.1 | 77 ft |
| Henry County | 12,300 | 42% | 2.3% | 0.0 | 75 ft |
| Van Wert County | 11,900 | 39% | 3.0% | 0.0 | 95 ft |
| Meigs County | 11,200 | 49% | 2.9% | 0.1 | 90 ft |
| Paulding County | 10,700 | 56% | 1.9% | 0.0 | 60 ft |
| Fayette County | 10,600 | 34% | 19.1% | 0.0 | 86 ft |
| Hamilton County | 10,400 | 1% | 4.6% | 0.7 | 55 ft |
| Wyandot County | 9,400 | 40% | 6.2% | 0.0 | 85 ft |
| Morgan County | 8,900 | 64% | 2.4% | 0.1 | 75 ft |
| Vinton County | 8,700 | 66% | 2.7% | 0.0 | 240 ft |
| Monroe County | 7,800 | 58% | 2.7% | 0.1 | 95 ft |
| Harrison County | 7,300 | 51% | 2.2% | 0.1 | 118 ft |
| Noble County | 6,500 | 56% | 2.0% | 0.1 | 83 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Wayne County: about 22,500 people
- Licking County: about 10,100 people
- Medina County: about 9,700 people
- Summit County: about 9,200 people
- Fairfield County: about 8,800 people
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Questions
Which Ohio counties rely most on wells?+
By share of homes: Geauga County (79%), Holmes County (67%), Carroll County (67%), Morrow County (67%), Vinton County (66%). By number of people: Stark County (122,800), Summit County (115,000), Geauga County (77,000).
Is arsenic a problem in Ohio wells?+
USGS estimates about 189,200 Ohio well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Wayne County, Licking County, Medina County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Ohio?+
We could not confirm a statewide rule for Ohio. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).