Well Water Nerd

Total coliform in well water

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

Coliform bacteria live in soil and on plants as well as in sewage. Their presence means surface water or soil is getting into the well through the cap, casing or a nearby defect. Most coliforms are harmless, but they mean disease-causing organisms can get in the same way.

EPA limit
0 MPN/100mL (EPA Revised Total Coliform Rule: any confirmed presence triggers assessment)
Pennsylvania level
0 MPN/100mL

Check your total coliform 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 total coliform

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 total coliform

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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 total coliform

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 total coliform 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, Pennsylvania106228 MPN/100mL
Clearfield County, Pennsylvania142517 MPN/100mL
Armstrong County, Pennsylvania124201 MPN/100mL
Cameron County, Pennsylvania119201 MPN/100mL
Washington County, Pennsylvania4181011 MPN/100mL
Jefferson County, Pennsylvania131201 MPN/100mL
Forest County, Pennsylvania81201 MPN/100mL
Fayette County, Pennsylvania141201 MPN/100mL
Elk County, Pennsylvania100687 MPN/100mL
McKean County, Pennsylvania542228 MPN/100mL
Indiana County, Pennsylvania1531414 MPN/100mL
Cambria County, Pennsylvania105457 MPN/100mL
Allegheny County, Pennsylvania308401 MPN/100mL
Westmoreland County, Pennsylvania7832420 MPN/100mL
Fulton County, Pennsylvania58201 MPN/100mL

By individual samples

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

CountyAbove EPA limitSamplesDetectedMedian
Lincoln County, Idaho5567%3 MPN/100mL
Nez Perce County, Idaho3735%0 MPN/100mL
Fremont County, Idaho6528%0 MPN/100mL
Minidoka County, Idaho4425%0 MPN/100mL
Ada County, Idaho16922%0 MPN/100mL
Owyhee County, Idaho12018%0 MPN/100mL
Elmore County, Idaho7318%0 MPN/100mL
Jefferson County, Idaho6316%0 MPN/100mL
Washington County, Idaho11815%0 MPN/100mL
Payette County, Idaho32915%0 MPN/100mL
Gem County, Idaho12713%0 MPN/100mL
Canyon County, Idaho60412%0 MPN/100mL
Teton County, Idaho329%0 MPN/100mL
Twin Falls County, Idaho10618%0 MPN/100mL
Kootenai County, Idaho480%0 MPN/100mL

How to test

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

How to treat

  • Inspect and repair the well cap and casing, then shock chlorinate and retest
  • UV disinfection whole-house
  • Chlorination system