E. coli in well water: what to do right now
E. coli means human or animal waste is reaching your water. Stop drinking it now: use bottled water, or boil water at a rolling boil for one minute, and call your local health department.
- US (EPA)
- Absent. Any E. coli is a reason to stop drinking the water.
- Ontario
- Not detectable. Public Health Ontario reports any E. coli as unsafe to drink.
What it is
E. coli lives in the gut of people and animals. Most types are harmless there, but finding it in well water shows fecal contamination, which can carry germs that cause serious stomach illness, especially for babies, older adults and anyone with a weak immune system.
What your number means
- Within limitsAbsent, or 0 per 100 mL
No E. coli was found in this sample.
- Act nowPresent, or any count
Unsafe to drink. Use bottled or boiled water, call your health department, disinfect the well and retest.
What to do
- Stop drinking the water. Use bottled water, or boil it at a rolling boil for at least one minute, for drinking, cooking, formula, ice and brushing teeth.
- Call your local health department. Many will help you find the source and plan next steps for free.
- Look for sources nearby: a septic system, manure, animals, or flooding near the well.
- Have the well inspected and disinfected by a licensed well contractor.
- Retest after disinfection. Keep using safe water until you get a clean result.
How often to test
After a positive result, retest until clean. Then test for bacteria every year in the US, and at least three times a year in Ontario.
Common questions
Can I shower with water that has E. coli?
Many health departments say healthy adults can shower if they avoid swallowing water, but ask yours, and use safe water for babies' baths.
Do water filters remove E. coli?
Only systems built for disinfection, like UV, are designed for bacteria, and they don't fix the source. Disinfect the well and find how waste gets in.
Is E. coli the same as total coliform?
No. E. coli is one type of coliform and the one that points to waste. Total coliform is a broader warning that surface water can reach the well.
Sources: EPA drinking water standards; Ontario Drinking Water Quality Standards, O. Reg. 169/03; Public Health Ontario well water testing. Limits checked October 2026.