Well water by county: Pennsylvania
Across 62 counties in Pennsylvania, 120 of 3072 sampled wells (4%) were above the arsenic limit and 539 of 6478 (8%) above the nitrate limit. Updated 2026-10-17. 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).
| County | Arsenic > 10 µg/L | Nitrate > 10 mg/L |
|---|---|---|
| Adams County | 3% of 32 | 7% of 98 |
| Allegheny County | 10% of 10 | 0% of 35 |
| Beaver County | – | 0% of 16 |
| Bedford County | 4% of 25 | 6% of 83 |
| Berks County | 7% of 71 | 8% of 191 |
| Blair County | 13% of 24 | 23% of 73 |
| Bradford County | 7% of 189 | 1% of 213 |
| Bucks County | 7% of 97 | 2% of 244 |
| Butler County | – | 0% of 17 |
| Cambria County | 0% of 14 | 0% of 28 |
| Cameron County | – | 0% of 16 |
| Centre County | 4% of 56 | 3% of 77 |
| Chester County | 0% of 452 | 10% of 858 |
| Clarion County | 23% of 35 | 1% of 104 |
| Clearfield County | 0% of 43 | 2% of 50 |
| Clinton County | 1% of 76 | 6% of 82 |
| Columbia County | 16% of 19 | 1% of 80 |
| Crawford County | – | 0% of 32 |
| Cumberland County | 0% of 25 | 13% of 172 |
| Dauphin County | 8% of 74 | 1% of 121 |
| Delaware County | 0% of 32 | 2% of 43 |
| Erie County | 30% of 33 | 4% of 109 |
| Fayette County | 0% of 12 | 7% of 28 |
| Franklin County | 0% of 43 | 10% of 67 |
| Fulton County | – | 5% of 21 |
| Greene County | 0% of 14 | 3% of 58 |
| Huntingdon County | 8% of 12 | 0% of 58 |
| Indiana County | 1% of 295 | 0% of 300 |
| Jefferson County | 0% of 43 | 0% of 55 |
| Juniata County | 0% of 10 | 0% of 27 |
| Lackawanna County | – | 0% of 43 |
| Lancaster County | 0% of 125 | 39% of 621 |
| Lawrence County | – | 0% of 29 |
| Lebanon County | 1% of 88 | 9% of 173 |
| Lehigh County | – | 2% of 161 |
| Luzerne County | 8% of 13 | 3% of 68 |
| Lycoming County | 8% of 113 | 1% of 130 |
| McKean County | – | 0% of 11 |
| Mercer County | – | 0% of 100 |
| Mifflin County | 0% of 12 | 13% of 46 |
| Monroe County | – | 0% of 28 |
| Montgomery County | 13% of 53 | 4% of 114 |
| Montour County | – | 0% of 33 |
| Northampton County | – | 21% of 29 |
| Northumberland County | 2% of 56 | 17% of 69 |
| Perry County | 0% of 24 | 4% of 85 |
| Philadelphia County | 8% of 75 | 11% of 195 |
| Pike County | 1% of 111 | 0% of 149 |
| Potter County | 3% of 98 | 0% of 92 |
| Schuylkill County | 2% of 45 | 2% of 86 |
| Snyder County | 6% of 31 | 2% of 41 |
| Somerset County | 0% of 30 | 0% of 49 |
| Sullivan County | 3% of 39 | 0% of 29 |
| Susquehanna County | 12% of 33 | 0% of 119 |
| Tioga County | 8% of 131 | 0% of 76 |
| Union County | 0% of 16 | 0% of 21 |
| Warren County | – | 0% of 90 |
| Washington County | 0% of 10 | 8% of 12 |
| Wayne County | 3% of 143 | 0% of 150 |
| Westmoreland County | – | 0% of 25 |
| Wyoming County | 4% of 23 | 2% of 47 |
| York County | 0% of 67 | 10% of 201 |