Positive for E. coli or coliform: next steps for a New York well
As of 2026-10-07. Limits come from US EPA and the New York State Department of Health (NYSDOH). Rules change; sources are linked below. Private wells aren't regulated like public water: NYSDOH uses public-water standards as guidelines for private wells.
Positive result? NYSDOH says to stop using your well water and use bottled water for drinking, preparing food, or making ice, and to contact your local health department (health.ny.gov/contact/contact_information/). NYSDOH advises boiling water until disinfection and retesting confirm the contamination is gone. If anyone has symptoms such as diarrhea or vomiting, talk to a health care provider.
This page is the follow-up to coliform in well water, which covers what the result means.
Total coliform vs. E. coli
NYSDOH: a positive total coliform sample "should be considered an indication of pollution in your well," and positive E. coli results "should be considered indication of fecal pollution." EPA says fecal coliforms and E. coli come only from human and animal fecal waste. NYSDOH says E. coli and coliform bacteria indicate fecal contamination that can cause symptoms such as diarrhea and vomiting.
The steps, in order (from NYSDOH guidance)
Use other water and call your local health department. Ask what it recommends for your situation.
Look for the cause. NYSDOH says a defective well is often the cause. It lists a missing or defective well cap, cracks or holes in the casing, seepage along the outside of the casing (many older wells weren't grouted), and flooding of wellheads in frost pits. Electrical safety first: NYSDOH says to shut off power to the pump before doing anything at the well. If the casing, cap, or pump needs repair, use a qualified professional, such as a DEC-registered well contractor.
Repair, then disinfect (shock-chlorinate) the well and plumbing. Follow NYSDOH's step-by-step disinfection method. NYSDOH calls for regular, unscented household bleach (not splashless, scented, or gel). It recommends hiring a water well contractor if you have a point well or a jet pump, and it advises extreme caution around electricity.
Flush the chlorinated water until the chlorine odor is gone. Follow NYSDOH's directions on where to run the hose.
Retest at an ELAP-certified lab once the water no longer smells of chlorine. NYSDOH says that if the odor persists, you may have to flush again or wait several days before testing. Get a sterile bottle from the lab and follow its instructions exactly. NYSDOH notes that improper sampling can give false results.
Keep using bottled water until the retest shows the water is free of contamination (NYSDOH).
Test again later. NYSDOH says one sample is "just a snapshot," and recommends testing more often if you've had bacteria problems before. After a flood, it suggests retesting after several weeks.
If it keeps coming back
NYSDOH's long-term options: connect to a public water system if possible; inspect the well for defects and repair them; build a new well; install continuous disinfection equipment; or use bottled water for drinking and food preparation.
Results show more than bacteria? The NY guide explains about two dozen common tests (nitrate, lead, arsenic, PFAS and more), with an urgency triage and a worksheet. See also nitrate and reading your results.