Well Water Nerd

E. coli in Pennsylvania well water

In Pennsylvania, 11% of 22,730 private wells tested between 2007 and 2025 had E. coli above the EPA limit (0 MPN/100mL), according to the Penn State water testing lab.

E. coli in a well means fecal contamination from septic systems, animals or surface water entering the well. It can cause serious gastrointestinal illness. Any detection is a failure.

Check your E. coli number

Type the value from your lab report. It is compared to the EPA limit and the EPA limit, the same way the full interpretation does it.

Test your Pennsylvania well for E. coli

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209Already tested? Upload the report

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Systems that remove E. coli

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Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For E. coli

UV disinfection system

whole-house, at the point of entry, about $900

Fix the well cap and casing first; UV keeps bacteria from returning.

For E. coli

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.

Where to get a well tested for E. coli in Pennsylvania: certified labs, state programs and prices.

By county, from homeowner tests

Share of private wells above the state guidance level (0 MPN/100mL) in tests homeowners sent to the state lab, 2008 to 2025.

CountyAbove state levelWells testedHighest
Greene106201 MPN/100mL
Washington418201 MPN/100mL
Clearfield142201 MPN/100mL
Jefferson131201 MPN/100mL
Clarion120201 MPN/100mL
Fayette141201 MPN/100mL
Cameron119201 MPN/100mL
Armstrong124201 MPN/100mL
Allegheny308401 MPN/100mL
Forest81201 MPN/100mL
Philadelphia89201 MPN/100mL
Cambria10573.8 MPN/100mL
Clinton449201 MPN/100mL
McKean542201 MPN/100mL
Schuylkill142201 MPN/100mL

By county, from individual samples

Public monitoring samples against the EPA limit (0 MPN/100mL); counties with at least 30 samples.

CountyAbove EPA limitSamplesDetectedMedianHighest
Potter4628%0125 MPN/100mL
Clinton6027%0140 MPN/100mL
Berks3222%095 MPN/100mL
Lycoming8412%0153 MPN/100mL
Lancaster427%010 MPN/100mL
Wayne1757%02 MPN/100mL
Cumberland329%0170 MPN/100mL
Bradford829%09 MPN/100mL
Pike1480%00 MPN/100mL

Sources

  • Penn State Agricultural Analytical Services Lab drinking water summaries: County summaries of private water samples tested by the Penn State Agricultural Analytical Services Laboratory since 2007, published by the College of Agricultural Sciences. Counts are samples, not distinct wells. Shares are against the standard the lab prints: the EPA maximum contaminant level, or the secondary standard for iron, manganese and chloride. Lead is the first-draw result. Medians printed as 0.00 are stored as null because the lab rounds to two decimals. Retrieved September 16, 2026.
  • Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. E. coli counts and shares are listed on each county and town page with their sources.