Coliform-positive well water: what it means and what to do next
Short answer: If total coliform is positive but E. coli is negative, the New Jersey Department of Health says to retest within the week and again six months later. If E. coli is positive or coliform keeps returning, find and fix the source, consider treatment or disinfection, and use bottled or boiled water until retesting shows it is safe.
What the result means
The CDC says coliform bacteria generally won't make you sick, but they get into water the same way as germs that do. A high total coliform count makes it likely that harmful germs are present. A positive fecal coliform or E. coli test likely means feces have entered the well. [source]
Next steps
| Result | What the NJ Department of Health advises |
|---|---|
| Total coliform positive, E. coli negative | Retest within the week and again six months later. |
| Repeated coliform positives, or any E. coli positive | Identify and correct possible sources, such as surface contamination or well construction defects, or install treatment. You may need a well professional. [source] |
Drinking water in the meantime
If your well is contaminated with germs, the CDC says to drink bottled water or water from another safe source, contact your local health department, and boil well water if you can't get a safe source. [source] The NJ Department of Health says boiling for at least one minute kills bacteria, though it may not work long term. [source]
Fixing it
- Shock chlorination: high-concentration chlorine for at least 12–24 hours, appropriate when the cause is likely a one-time event such as flooding or a nearby well being drilled. [source]
- Treatment: ultraviolet light or ozone systems, maintained per the manufacturer's instructions. [source]
- Retest before drinking untreated water, then again in 6 months to a year, per Mississippi State University Extension. [source] The CDC says to test after treatment to make sure it worked. [source]
Was it a sampling error?
Mississippi State Extension notes the first sample may have been contaminated during collection. Follow the lab's instructions, remove aerators or filters, and don't touch the inside of the bottle or cap. [source] See our sampling guide.
FAQ
What should I do if my well tests positive for coliform?
If total coliform is positive but E. coli is negative, the New Jersey Department of Health says to retest within the week and again six months later. If E. coli is positive or coliform keeps returning, find and fix the source, consider treatment or disinfection, and use bottled or boiled water until retesting shows it is safe.
Can I drink my well water if it tests positive for total coliform?
The CDC says to drink bottled or other safe water if your well is contaminated with germs and to contact your local health department. Mississippi State Extension advises bottled water until a retest is back.
How long does shock chlorination take?
The NJ Department of Health describes shock chlorination as high concentrations of chlorine for at least 12 to 24 hours.
Sources
- CDC – Guidelines for Testing Well Water (accessed 2026-10-23)
- CDC – Guidelines for Treating Well Water (accessed 2026-10-23)
- NJ Department of Health – Total Coliform & E. coli in Private Well Drinking Water (PDF) (accessed 2026-10-23)
- Mississippi State University Extension – What to Do about Coliform Bacteria in Well Water (accessed 2026-10-23)
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