Private wells
Pennsylvania well water: who's on a well and what to test for
People on private wells
2,400,800
Homes on wells
18.5%
Est. above arsenic limit
80,700
Every Pennsylvania 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.
| Lancaster County | 172,400 | 28% | 2.3% | 8.7 | 133 ft |
| Chester County | 117,800 | 21% | 3.0% | 5.3 | 118 ft |
| York County | 116,300 | 25% | 3.3% | 3.4 | 101 ft |
| Berks County | 107,000 | 25% | 4.9% | 3.4 | 140 ft |
| Bucks County | 101,800 | 16% | 7.9% | 1.8 | 140 ft |
| Monroe County | 89,700 | 56% | 2.5% | 0.6 | n/a |
| Montgomery County | 74,000 | 8% | 10.1% | 1.8 | 160 ft |
| Butler County | 72,500 | 36% | 3.3% | 0.1 | n/a |
| Dauphin County | 59,100 | 20% | 5.0% | 1.5 | n/a |
| Cumberland County | 58,200 | 21% | 1.8% | 3.2 | 170 ft |
| Luzerne County | 57,500 | 17% | 4.8% | 0.2 | n/a |
| Erie County | 57,400 | 20% | 12.1% | 0.2 | 46 ft |
| Lehigh County | 55,000 | 15% | 4.0% | 3.3 | 110 ft |
| Northampton County | 54,300 | 18% | 2.7% | 3.2 | n/a |
| Franklin County | 52,600 | 32% | 2.1% | 3.8 | n/a |
| Crawford County | 51,900 | 63% | 7.6% | 0.1 | n/a |
| Mercer County | 45,300 | 40% | 15.7% | 0.0 | 76 ft |
| Adams County | 40,800 | 39% | 4.5% | 1.4 | 160 ft |
| Lycoming County | 40,500 | 35% | 2.7% | 0.3 | n/a |
| Lebanon County | 39,900 | 27% | 2.5% | 4.8 | 107 ft |
| Schuylkill County | 37,000 | 25% | 4.6% | 0.8 | 100 ft |
| Bradford County | 35,700 | 60% | 6.7% | 0.1 | 82 ft |
| Beaver County | 34,400 | 19% | 3.2% | 0.1 | n/a |
| Bedford County | 33,800 | 70% | 2.8% | 0.5 | n/a |
| Lawrence County | 33,000 | 37% | 5.8% | 0.1 | n/a |
| Wayne County | 31,100 | 61% | 6.4% | 0.2 | n/a |
| Perry County | 31,100 | 66% | 4.7% | 0.5 | n/a |
| Lackawanna County | 29,600 | 14% | 5.0% | 0.3 | n/a |
| Pike County | 29,300 | 51% | 2.3% | 0.2 | 175 ft |
| Somerset County | 29,200 | 39% | 2.0% | 0.2 | n/a |
| Carbon County | 28,700 | 47% | 4.2% | 0.4 | n/a |
| Columbia County | 27,500 | 43% | 4.4% | 0.5 | n/a |
| Susquehanna County | 25,900 | 69% | 6.5% | 0.2 | n/a |
| Westmoreland County | 25,400 | 7% | 1.9% | 0.2 | n/a |
| Blair County | 24,800 | 19% | 1.9% | 0.9 | n/a |
| Northumberland County | 24,400 | 24% | 6.0% | 0.8 | n/a |
| Tioga County | 24,400 | 61% | 6.1% | 0.1 | 100 ft |
| Centre County | 23,600 | 15% | 1.5% | 1.2 | n/a |
| Indiana County | 23,200 | 26% | 1.8% | 0.2 | 110 ft |
| Washington County | 22,900 | 11% | 2.5% | 0.2 | 98 ft |
| Allegheny County | 22,100 | 2% | 2.6% | 0.3 | n/a |
| Huntingdon County | 21,700 | 56% | 5.9% | 0.4 | n/a |
| Venango County | 21,000 | 43% | 2.3% | 0.1 | n/a |
| Jefferson County | 20,300 | 45% | 1.6% | 0.1 | n/a |
| Snyder County | 20,300 | 50% | 5.2% | 0.7 | n/a |
| Warren County | 19,300 | 54% | 3.5% | 0.1 | n/a |
| Armstrong County | 18,800 | 28% | 2.0% | 0.1 | n/a |
| Cambria County | 17,900 | 12% | 1.6% | 0.2 | n/a |
| Clarion County | 17,800 | 50% | 1.5% | 0.2 | 85 ft |
| Wyoming County | 17,700 | 70% | 6.7% | 0.1 | n/a |
| Mifflin County | 16,600 | 35% | 5.1% | 1.0 | n/a |
| Union County | 16,500 | 43% | 7.0% | 1.4 | n/a |
| McKean County | 15,300 | 39% | 4.0% | 0.1 | n/a |
| Juniata County | 15,100 | 61% | 5.5% | 0.9 | n/a |
| Clearfield County | 13,900 | 19% | 1.8% | 0.1 | n/a |
| Delaware County | 11,100 | 2% | 2.3% | 2.1 | n/a |
| Fulton County | 10,700 | 73% | 4.9% | 0.3 | n/a |
| Potter County | 9,500 | 63% | 6.0% | 0.1 | 100 ft |
| Fayette County | 9,400 | 8% | 1.7% | 0.1 | n/a |
| Greene County | 9,200 | 28% | 2.3% | 0.1 | n/a |
| Clinton County | 8,600 | 26% | 2.5% | 0.6 | n/a |
| Montour County | 8,500 | 43% | 5.7% | 0.6 | n/a |
| Elk County | 6,100 | 27% | 1.9% | 0.1 | n/a |
| Forest County | 5,600 | 82% | 1.6% | 0.1 | n/a |
| Sullivan County | 4,600 | 84% | 2.9% | 0.1 | n/a |
| Philadelphia County | 2,600 | 0% | 4.5% | 1.4 | n/a |
| Cameron County | 1,600 | 54% | 2.9% | 0.1 | n/a |
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
- Crawford County: about 6,000 people
- Erie County: about 5,900 people
- Montgomery County: about 4,100 people
- Mercer County: about 4,100 people
- Lancaster County: about 3,700 people
Highest modeled nitrate
- Lancaster County: 8.7 mg/L average (limit 10)
- Chester County: 5.3 mg/L average (limit 10)
- Lebanon County: 4.8 mg/L average (limit 10)
- Franklin County: 3.8 mg/L average (limit 10)
- York County: 3.4 mg/L average (limit 10)
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.
Mail-in certified lab well water test
Mid-range2. 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.
5-micron whole-house sediment filter
Budget3. 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.
Air-injection iron and sulfur filter
Premium4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
12 GPM whole-house UV purifier
Premium5. 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.
Waterdrop G3P600 tankless RO
Price at Waterdrop, checked Oct 5, 2026or compare on Amazon
iSpring RCC7AK reverse osmosis
Mid-range6. 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.
Waterdrop WHF21 2-stage whole-house filter
Mid-rangeQuestions
Which Pennsylvania counties rely most on wells?+
By share of homes: Sullivan County (84%), Forest County (82%), Fulton County (73%), Bedford County (70%), Wyoming County (70%). By number of people: Lancaster County (172,400), Chester County (117,800), York County (116,300).
Is arsenic a problem in Pennsylvania wells?+
USGS estimates about 80,700 Pennsylvania well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Crawford County, Erie County, Montgomery 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 Pennsylvania?+
We could not confirm a statewide rule for Pennsylvania. 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).