Well Water Nerd

E. coli in well water

1in3

private wells tested in Greene County, Pennsylvania had e. coli above the limit, the highest share of any county, according to Penn State Agricultural Analytical Services Lab drinking water summaries.

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.

EPA limit
0 MPN/100mL (EPA MCL: any confirmed presence (40 CFR 141.63))
Pennsylvania level
0 MPN/100mL

Check your E. coli number

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

Test your own 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

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says.

Systems that remove E. coli

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.

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 e. coli is worst, by homeowner tests

Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.

CountyAbove state levelWells testedHighest
Greene County, Pennsylvania106201 MPN/100mL
Washington County, Pennsylvania418201 MPN/100mL
Clearfield County, Pennsylvania142201 MPN/100mL
Jefferson County, Pennsylvania131201 MPN/100mL
Clarion County, Pennsylvania120201 MPN/100mL
Fayette County, Pennsylvania141201 MPN/100mL
Cameron County, Pennsylvania119201 MPN/100mL
Armstrong County, Pennsylvania124201 MPN/100mL
Allegheny County, Pennsylvania308401 MPN/100mL
Forest County, Pennsylvania81201 MPN/100mL
Philadelphia County, Pennsylvania89201 MPN/100mL
Cambria County, Pennsylvania10573.8 MPN/100mL
Clinton County, Pennsylvania449201 MPN/100mL
McKean County, Pennsylvania542201 MPN/100mL
Schuylkill County, Pennsylvania142201 MPN/100mL

By individual samples

Counties with at least 30 individual samples in public monitoring data, against the EPA limit.

CountyAbove EPA limitSamplesDetectedMedian
Potter County, Pennsylvania4628%0 MPN/100mL
Jackson County, Kansas8826%0 MPN/100mL
Clinton County, Pennsylvania6027%0 MPN/100mL
Santa Barbara County, California6321%0 MPN/100mL
Orange County, North Carolina5018%0 MPN/100mL
Berks County, Pennsylvania3222%0 MPN/100mL
Lycoming County, Pennsylvania8412%0 MPN/100mL
Bexar County, Texas7011%0 MPN/100mL
Whatcom County, Washington29910%0 MPN/100mL
Linn County, Iowa697%0 MPN/100mL
Lancaster County, Pennsylvania427%0 MPN/100mL
Suffolk County, New York467%0 MPN/100mL
Wayne County, Pennsylvania1757%0 MPN/100mL
Cumberland County, Pennsylvania329%0 MPN/100mL
Butte County, Idaho385%0 MPN/100mL

How to test

Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure e. coli at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.

How to treat

  • Shock chlorination and fix the well cap or casing
  • UV disinfection whole-house
  • Chlorination system