Pennsylvania well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Pennsylvania county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 67 counties
- Lancaster CountyWell users 130,400Arsenic about 2 in 100Nitrate 8.7 mg/L
- Chester CountyWell users 112,200Arsenic about 3 in 100Nitrate 5.3 mg/L
- Bucks CountyWell users 104,400Arsenic about 8 in 100Nitrate 1.8 mg/L
- York CountyWell users 94,800Arsenic about 3 in 100Nitrate 3.4 mg/L
- Berks CountyWell users 91,000Arsenic about 5 in 100Nitrate 3.4 mg/L
- Montgomery CountyWell users 69,600Arsenic about 10 in 100Nitrate 1.8 mg/L
- Butler CountyWell users 61,500Arsenic about 3 in 100Nitrate 0.1 mg/L
- Erie CountyWell users 59,000Arsenic about 12 in 100Nitrate 0.2 mg/L
- Luzerne CountyWell users 54,100Arsenic about 5 in 100Nitrate 0.2 mg/L
- Westmoreland CountyWell users 52,500Arsenic about 2 in 100Nitrate 0.2 mg/L
- Crawford CountyWell users 52,200Arsenic about 8 in 100Nitrate 0.1 mg/L
- Dauphin CountyWell users 52,100Arsenic about 5 in 100Nitrate 1.5 mg/L
- Monroe CountyWell users 49,300Arsenic about 2 in 100Nitrate 0.6 mg/L
- Cumberland CountyWell users 48,500Arsenic about 2 in 100Nitrate 3.2 mg/L
- Mercer CountyWell users 45,100Arsenic about 16 in 100Nitrate 0.0 mg/L
- Lehigh CountyWell users 39,600Arsenic about 4 in 100Nitrate 3.3 mg/L
- Lycoming CountyWell users 37,500Arsenic about 3 in 100Nitrate 0.3 mg/L
- Northampton CountyWell users 37,000Arsenic about 3 in 100Nitrate 3.2 mg/L
- Schuylkill CountyWell users 36,600Arsenic about 5 in 100Nitrate 0.8 mg/L
- Adams CountyWell users 36,000Arsenic about 4 in 100Nitrate 1.4 mg/L
- Bradford CountyWell users 35,200Arsenic about 7 in 100Nitrate 0.1 mg/L
- Franklin CountyWell users 34,900Arsenic about 2 in 100Nitrate 3.8 mg/L
- Beaver CountyWell users 34,000Arsenic about 3 in 100Nitrate 0.1 mg/L
- Washington CountyWell users 33,400Arsenic about 3 in 100Nitrate 0.2 mg/L
- Indiana CountyWell users 32,900Arsenic about 2 in 100Nitrate 0.2 mg/L
- Wayne CountyWell users 30,800Arsenic about 6 in 100Nitrate 0.2 mg/L
- Lawrence CountyWell users 30,200Arsenic about 6 in 100Nitrate 0.1 mg/L
- Blair CountyWell users 30,200Arsenic about 2 in 100Nitrate 0.9 mg/L
- Lebanon CountyWell users 29,900Arsenic about 2 in 100Nitrate 4.8 mg/L
- Bedford CountyWell users 29,500Arsenic about 3 in 100Nitrate 0.5 mg/L
- Perry CountyWell users 28,600Arsenic about 5 in 100Nitrate 0.5 mg/L
- Lackawanna CountyWell users 27,300Arsenic about 5 in 100Nitrate 0.3 mg/L
- Susquehanna CountyWell users 27,100Arsenic about 7 in 100Nitrate 0.2 mg/L
- Columbia CountyWell users 26,300Arsenic about 4 in 100Nitrate 0.5 mg/L
- Allegheny CountyWell users 26,100Arsenic about 3 in 100Nitrate 0.3 mg/L
- Somerset CountyWell users 26,000Arsenic about 2 in 100Nitrate 0.2 mg/L
- Armstrong CountyWell users 25,100Arsenic about 2 in 100Nitrate 0.1 mg/L
- Northumberland CountyWell users 24,100Arsenic about 6 in 100Nitrate 0.8 mg/L
- Huntingdon CountyWell users 22,600Arsenic about 6 in 100Nitrate 0.4 mg/L
- Tioga CountyWell users 22,300Arsenic about 6 in 100Nitrate 0.1 mg/L
- Pike CountyWell users 22,100Arsenic about 2 in 100Nitrate 0.2 mg/L
- Carbon CountyWell users 21,400Arsenic about 4 in 100Nitrate 0.4 mg/L
- Centre CountyWell users 20,500Arsenic about 2 in 100Nitrate 1.2 mg/L
- Venango CountyWell users 20,100Arsenic about 2 in 100Nitrate 0.1 mg/L
- Cambria CountyWell users 19,600Arsenic about 2 in 100Nitrate 0.2 mg/L
- Warren CountyWell users 19,500Arsenic about 3 in 100Nitrate 0.1 mg/L
- Union CountyWell users 19,500Arsenic about 7 in 100Nitrate 1.4 mg/L
- Wyoming CountyWell users 18,200Arsenic about 7 in 100Nitrate 0.1 mg/L
- Fayette CountyWell users 18,000Arsenic about 2 in 100Nitrate 0.1 mg/L
- Snyder CountyWell users 17,500Arsenic about 5 in 100Nitrate 0.7 mg/L
- Mifflin CountyWell users 16,700Arsenic about 5 in 100Nitrate 1.0 mg/L
- Jefferson CountyWell users 16,200Arsenic about 2 in 100Nitrate 0.1 mg/L
- Delaware CountyWell users 15,300Arsenic about 2 in 100Nitrate 2.1 mg/L
- Juniata CountyWell users 15,300Arsenic about 6 in 100Nitrate 0.9 mg/L
- Clearfield CountyWell users 15,000Arsenic about 2 in 100Nitrate 0.1 mg/L
- Clarion CountyWell users 13,900Arsenic about 1 in 100Nitrate 0.2 mg/L
- McKean CountyWell users 12,800Arsenic about 4 in 100Nitrate 0.1 mg/L
- Fulton CountyWell users 10,800Arsenic about 5 in 100Nitrate 0.2 mg/L
- Montour CountyWell users 9,000Arsenic about 6 in 100Nitrate 0.6 mg/L
- Greene CountyWell users 8,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- Potter CountyWell users 7,400Arsenic about 6 in 100Nitrate 0.1 mg/L
- Clinton CountyWell users 6,900Arsenic about 2 in 100Nitrate 0.6 mg/L
- Elk CountyWell users 5,100Arsenic about 2 in 100Nitrate 0.1 mg/L
- Sullivan CountyWell users 4,800Arsenic about 3 in 100Nitrate 0.1 mg/L
- Forest CountyWell users 3,800Arsenic about 2 in 100Nitrate 0.1 mg/L
- Philadelphia CountyWell users 3,000Arsenic about 5 in 100Nitrate 1.4 mg/L
- Cameron CountyWell users 1,300Arsenic about 3 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
Pennsylvania Department of Environmental Protection lists the laboratories certified to test drinking water in Pennsylvania.
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.
Pennsylvania 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 Pennsylvania?
About 2.2 million people across 67 Pennsylvania counties, by the USGS 2010 estimate. USGS models place about 100,200 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 Pennsylvania?
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 Pennsylvania?
Pennsylvania Department of Environmental Protection keeps the list of laboratories certified to test drinking water in Pennsylvania. Only use laboratories that are certified to do drinking water testing. (EPA)