Coliform Bacteria in Well Water
Total coliform present means something from the surface is getting into your well. E. coli present means it is sewage or manure. The fix is usually the wellhead, not a filter.
Likely causes
- Cracked or shallow casing
- Missing or damaged well cap
- Surface water pooling at the wellhead
- Septic system too close or failing
- Recent repairs without disinfection
Tests to order
- Total coliform
- E. coli
- Nitrate
- Resample after shock chlorination
Treatment options
- Shock chlorination
- Repair the cap and casing seal
- Grade soil away from the well
- UV disinfection system
- Continuous chlorination for repeat failures
Total coliform versus E. coli
Total coliform is a family of bacteria that live in soil, on plants and in animal guts. Finding them means the well is not sealed from the surface. E. coli is a specific member that lives only in intestines, so a positive E. coli result means human or animal waste is reaching the water. Both are reported as present or absent, not as a count.
Walk out to the wellhead
Most coliform problems are visible from above ground. The cap should be a bolted, vermin-proof cap with a screened vent, not a loose steel plate. The casing should stand at least 12 inches above grade with soil sloping away. Look for insects around the cap, a septic tank or drain field uphill within 50 feet, or a buried wellhead in a pit. Any one of those is your cause.
Disinfect, fix, retest, in that order
Shock chlorination pours enough household bleach into the well to hold 50 to 200 ppm of chlorine for 12 to 24 hours, then flushes it out. Instructions are on every state health department site and the job costs under $30. Do the physical fix at the same time, then resample a week after the chlorine is gone. If the well fails again with the wellhead sound, install a UV disinfection unit, $500 to $1,200 installed, which kills bacteria continuously without chemicals. UV needs a sediment filter ahead of it and low iron to work.
Can I drink the water after boiling?
Boiling for one minute kills coliform and E. coli, so yes for the short term. It does nothing for whatever else may be coming in with the surface water.
Why did my well pass last year and fail now?
Wet seasons push more surface water underground, caps crack, and older casings corrode. Yearly testing exists exactly because wells change.