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privatewelldata / Counties

Well water by county: Ohio

Across 34 counties in Ohio, 91 of 620 sampled wells (15%) were above the arsenic limit and 15 of 1239 (1%) above the nitrate limit. Updated 2026-10-18. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.

Share of sampled wells whose latest result is above the EPA limit (arsenic 10 µg/L, nitrate 10 mg/L as N).

Share of sampled wells above the limit, by county (% of wells). Source: USGS/EPA Water Quality Portal · privatewelldata.com
CountyArsenic > 10 µg/LNitrate > 10 mg/L
Allen County–0% of 11
Athens County–6% of 18
Butler County0% of 232% of 85
Champaign County0% of 216% of 18
Clark County4% of 250% of 25
Coshocton County13% of 320% of 31
Darke County58% of 19–
Franklin County13% of 602% of 117
Geauga County16% of 310% of 75
Greene County20% of 202% of 63
Guernsey County–0% of 27
Hamilton County6% of 174% of 26
Hocking County–0% of 13
Jefferson County0% of 120% of 19
Licking County53% of 190% of 21
Lucas County0% of 332% of 55
Miami County14% of 210% of 40
Montgomery County12% of 341% of 143
Morgan County–12% of 17
Muskingum County21% of 283% of 36
Perry County–0% of 11
Pickaway County–0% of 13
Pike County–2% of 49
Preble County44% of 390% of 41
Sandusky County–0% of 47
Shelby County31% of 350% of 34
Stark County23% of 13–
Tuscarawas County0% of 400% of 42
Union County0% of 170% of 17
Vinton County–0% of 22
Warren County–0% of 13
Washington County–0% of 14
Williams County15% of 130% of 27
Wood County1% of 681% of 69