privatewelldata / Guides / Bacteria (total coliform and E. coli)

What to do if bacteria are found in your well

Total coliforms mean your water might not be safe; E. coli means it is not safe to drink.

Why it matters: E. coli is a sign of contamination by sewage or animal waste. If a sample contains any E. coli, do not drink the water. ^{[Health Canada]}
US limit: Goal: zero total coliforms (EPA MCLG). ^{[US EPA]}
Canada limit: None detectable per 100 mL. ^{[Health Canada]}

1. Right away

If the lab found E. coli: until a retest comes back clean, use bottled or other safe water, or keep well water at a hard boil for a full minute before using it to drink, cook or brush teeth. ^{[Health Canada],[Health Canada]}
If only total coliforms were found, Health Canada says you can keep using the water while you wait for more results. ^{[Health Canada]}
If someone at home has stomach illness you think is linked to the water, talk to your doctor and your local health unit. ^{[Health Canada]}

Test another sample as soon as possible. If it is clean, test a third to be sure. If the second or third confirms contamination, shock-disinfect the well. ^{[Health Canada]}

Inspect the well: cap secure and watertight, vent screened, ground sloping away, at least 3 m of trimmed grass around it, no cracks or gaps around the casing. ^{[Health Canada]}

Use unscented household bleach (not pool or hot-tub products). Bypass softeners, filters and reverse-osmosis units. Turn off pump power before opening the well. ^{[Health Canada],[CDC]}
Pour in the bleach, recirculate with a garden hose for 30 minutes, run every tap until you smell chlorine, then let it sit 12 to 24 hours without using the water. ^{[Health Canada]}
Flush outdoors until the chlorine smell is gone, away from plants, septic systems and streams. Health Canada’s bleach amounts by well depth and diameter are in its guide. ^{[Health Canada],[CDC]}
If it is your first time, you can hire a licensed well contractor. ^{[Health Canada]}

Health Canada: sample after 48 hours; the treatment probably worked after 2 safe results in a row over 1 to 3 weeks; test once more after 3 to 4 months. CDC: wait at least 7 to 10 days, once all chlorine is gone. ^{[Health Canada],[CDC]}
If it keeps coming back, repeat the shock treatment, contact your health unit, and consider a certified UV system (NSF/ANSI 55 Class A, with a filter before it). ^{[Health Canada]}

Who to call: in the US, contact your county or state health or environment agency (EPA lists them by state). In Canada, contact your local public health office or the provincial drinking-water authority. ^{[US EPA],[CDC],[Health Canada]}

General information, not medical advice.