Total coliform in New Jersey well water

In New Jersey, 15% of 140,846 private wells tested between 2002 and 2024 had total coliform above the New Jersey limit (any detection) (n/a MPN/100mL), according to NJDEP.

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.

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.

Getting it fixed

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

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
Warren	7,031	26%
Sussex	14,788	26%
Somerset	7,433	24%
Hunterdon	13,686	23%
Passaic	5,835	22%
Mercer	3,465	20%
Morris	13,108	20%
Union	84	18%
Middlesex	1,221	18%
Salem	5,046	11%
Bergen	3,555	11%
Monmouth	7,572	11%
Essex	231	11%
Gloucester	9,139	11%
Burlington	12,087	9%

Towns with the highest share above the state level

Califon borough, Hunterdon County41% of 37 wells
Franklin township, Hunterdon County35% of 589 wells
Frelinghuysen township, Warren County35% of 363 wells
Millstone borough, Somerset County34% of 32 wells
Hope township, Warren County34% of 359 wells
Lambertville, Hunterdon County34% of 122 wells
Stillwater township, Sussex County31% of 627 wells
Pennsville township, Salem County31% of 39 wells
Watchung borough, Somerset County30% of 171 wells
Mine Hill township, Morris County30% of 56 wells
Fredon township, Sussex County30% of 469 wells
Wantage township, Sussex County30% of 1,589 wells
Green township, Sussex County29% of 589 wells
South Brunswick township, Middlesex County29% of 96 wells
Frankford township, Sussex County29% of 999 wells
Woodland Park borough, Passaic County29% of 55 wells
Bridgewater township, Somerset County29% of 1,432 wells
Hopatcong borough, Sussex County29% of 2,183 wells
Deptford township, Gloucester County29% of 70 wells
Princeton, Mercer County29% of 56 wells
Mansfield township, Warren County28% of 620 wells
Blairstown township, Warren County28% of 969 wells
Franklin township, Warren County28% of 372 wells
Lafayette township, Sussex County28% of 339 wells
Hampton township, Sussex County28% of 774 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.