My Well Tested Positive for Coliform: What Now?

You sent in a water sample from your well, and the report came back "Total Coliform: Present." It's an unsettling result, but it's also one of the most common findings for private wells, and it's usually fixable. Here's what it means and what to do next.

Total coliform vs. E. coli: what your result means

Your report will usually list two results. Which one is positive makes a big difference.

Result	What it means	How urgent
Total coliform present, E. coli absent	Coliform bacteria are common in soil and surface water. Most aren't harmful themselves, but finding them means something is letting surface water or soil into your well.	Act promptly. Fix the source and disinfect.
E. coli present	E. coli comes from human or animal waste. It means fecal contamination, which can carry bacteria, viruses, and parasites that cause illness.	Stop drinking the water now.

Think of total coliform as a warning light: it tells you there's an opening in your well's defenses, even if nothing dangerous has come through yet.

E. coli bacteria, magnified 10,000×. Photo: Eric Erbe and Christopher Pooley, USDA Agricultural Research Service.

What to do now, step by step

Use safe water for drinking and cooking. If E. coli was found, use bottled water, or bring tap water to a rolling boil for 1 minute. With total coliform only, doing the same until you've disinfected and retested is a sensible precaution.

Look for the cause:

• Loose, cracked or missing well cap

• Cracks in the casing or casing at/below ground level

• Standing water or ground sloping toward the wellhead

• Recent flooding, runoff or snowmelt

• Recent work on the well, pump or plumbing

• Nearby septic system, drain field or animal area

Fix what you find. A new sanitary well cap or regrading the soil around the wellhead often solves the problem. Structural problems call for a licensed well driller.

Disinfect the well. Shock chlorination kills bacteria in the well and plumbing. Follow our guide: How to Disinfect a Small Water System.

Retest, but not too soon. Wait until chlorine is completely flushed out, usually at least a week after disinfecting. Keep the sample cool and get it to the lab within 24 hours.

Confirm it stays clean. Once you get an "Absent" result, retest in a few months, then at least once a year.

What if coliform keeps coming back?

• Have a licensed well driller inspect the casing, grout and seals.

• Install continuous treatment such as UV disinfection or chlorination.

• Test for nitrate and other indicators.

  
  

Operate a public water system?

Rules are different for public water systems. A positive sample triggers required repeat samples and reporting. Contact us or your state drinking water program right away.

Retest your well with Accurate Testing Labs

Accurate Testing Labs is a certified drinking water laboratory in Coeur d'Alene, testing for wells and water systems across North Idaho and Eastern Washington. Pick up sterile sample bottles at our lab, then bring your sample back within 30 hours.

7950 Meadowlark Way, Coeur d'Alene, ID 83815Phone: 208-762-8378 Monday–Friday, 7:00 am–3:00 pm. Weekends by appointment.

Not sure which tests your well needs? Call us before you sample, and we'll help you get it right the first time.