E. coli in New Jersey well water

In New Jersey, 2% of 140,562 private wells tested between 2002 and 2024 had E. coli above the New Jersey limit (any detection) (n/a MPN/100mL), according to NJDEP.

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, the same way the full interpretation does it.

Getting it fixed

Book a free in-home water test with a licensed local company, or see the treatment guide for what removes E. coli.

By county, from homeowner tests

Share of private wells above the state guidance level (n/a MPN/100mL) in tests homeowners sent to the state lab, 2002 to 2024.

County	Wells tested	Above state level
Somerset	7,423	4%
Union	84	4%
Sussex	14,704	4%
Hunterdon	13,655	3%
Passaic	5,809	3%
Mercer	3,454	3%
Warren	7,007	3%
Middlesex	1,216	2%
Morris	13,065	2%
Bergen	3,527	1%
Ocean	9,080	<1%
Monmouth	7,568	<1%
Cape May	7,329	<1%
Salem	5,044	<1%
Burlington	12,079	<1%

Towns with the highest share above the state level

Watchung borough, Somerset County10% of 171 wells
Millstone borough, Somerset County9% of 32 wells
Mine Hill township, Morris County9% of 56 wells
Princeton, Mercer County9% of 56 wells
Franklin township, Hunterdon County9% of 586 wells
Lambertville, Hunterdon County7% of 122 wells
Cherry Hill township, Camden County7% of 30 wells
Lafayette township, Sussex County7% of 340 wells
Burlington township, Burlington County6% of 47 wells
South Brunswick township, Middlesex County6% of 96 wells
Bridgewater township, Somerset County6% of 1,430 wells
Frelinghuysen township, Warren County6% of 359 wells
Mount Arlington borough, Morris County6% of 132 wells
Branchburg township, Somerset County6% of 711 wells
Pohatcong township, Warren County6% of 211 wells
Woodland Park borough, Passaic County6% of 53 wells
Califon borough, Hunterdon County5% of 37 wells
South Bound Brook borough, Somerset County5% of 38 wells
Bloomingdale borough, Passaic County5% of 254 wells
Lincoln Park borough, Morris County5% of 59 wells
Green township, Sussex County5% of 584 wells
Hampton township, Sussex County5% of 769 wells
Warren township, Somerset County5% of 612 wells
Readington township, Hunterdon County5% of 2,060 wells
Wantage township, Sussex County4% of 1,572 wells

Sources

NJDEP Private Well Testing Act summaries: Share of private wells exceeding each standard in tests required at sale or lease under the New Jersey Private Well Testing Act, September 2002 to December 2024, published by NJDEP. Tests are untreated water at the time of sale or lease, so every well is counted once per transaction. Municipalities with fewer than ten wells are suppressed. Standards are New Jersey's: arsenic 5 ug/L, PFOA 14 ng/L, PFOS 13 ng/L, PFNA 13 ng/L, manganese and iron secondary standards. Uranium and PFAS were added to the required panel in 2021 and 2020, so their well counts are smaller. Retrieved September 9, 2026.