Total coliform tells you something has a way in. E. coli tells you what is using it.
E. coli lives in the intestines of warm-blooded animals. Finding it in your well means fecal material is reaching your water — from a septic system, livestock, wildlife, or surface runoff. Everything else on the lab report can wait until tomorrow. This one changes what you do tonight.
The First Hour
Stop drinking the water. Everyone in the house, including pets.
Switch to bottled water, or boil properly: a rolling boil for one minute, or three minutes above 6,500 feet. Use boiled or bottled water for drinking, cooking, making ice, brushing teeth, and washing produce eaten raw.
Tell everyone in the house, and anyone who visits regularly. A note on the kitchen tap is not overkill — the failure mode here is a guest filling a glass without thinking.
Showering and bathing are generally fine for adults without open wounds, as long as you do not swallow the water. Be careful with infants and small children, who reliably drink bath water. Dishwashers on a hot cycle with a heated dry are usually acceptable; hand-washed dishes should be rinsed in boiled or bottled water and air-dried.
Then call your local health department. They deal with this constantly, they know the local aquifer and the local failure patterns, and in many areas they will help with follow-up testing.
Why This Is Worse Than a Coliform Hit
Both are "presence/absence" tests, and any detection is a fail. The difference is what the detection implies.
Total coliform bacteria are widespread in soil, vegetation and surface water. A positive result means your well is not sealed from the surface — a real problem, but the bacteria themselves are usually harmless.
E. coli is specific to intestinal origin. Its presence means the pathway is carrying fecal contamination, and where fecal contamination goes, so can pathogens capable of causing serious illness — particularly in young children, older adults, pregnant women, and anyone immunocompromised.
The lab is not telling you your water is dirty. It is telling you where the dirt is coming from.
Finding the Pathway
Shock chlorination will clear what is in the well today. If you stop there, you have treated the symptom and left the cause — which is why repeat positives are so common.
While the water is off-limits, go looking:
At the wellhead
- Is the cap intact, sealed, and vermin-proof? A cracked cap is a $40 part and a very common answer.
- Does the casing stand at least 12 inches above grade?
- Does the ground slope away from the well, or does water pond around it?
- Is the well in a pit? Pits flood, and they are a code violation in most states now.
- Any visible damage to the casing?
Nearby
- Recent flooding or heavy rain, especially if water reached the wellhead
- Septic tank or drain field condition, and the distance from the well
- Livestock, manure storage, or wildlife pressure upslope
- Any recent work on the well, the pump, or the plumbing
In the well's history
- How deep is it, and how deep is the casing? Shallow and dug wells are far more vulnerable than deep drilled ones.
- When was it last serviced, and did anything change shortly before the positive result?
Treat, Then Verify
Once you have found and fixed what you can:
- Shock chlorinate the well and the plumbing system.
- Flush thoroughly until the chlorine is gone — chlorine in the sample invalidates the retest.
- Retest for both total coliform and E. coli. Not one or the other.
- Retest again a few weeks later. A single clean result immediately after chlorination can simply mean the chlorine worked; the second test tells you whether the pathway is closed.
- Then test again at the next seasonal change, particularly after the first heavy rain.
If E. coli returns after a proper shock, stop reaching for bleach. Repeat positives indicate a structural problem — a failed seal, a cracked casing, an inadequate grout job, or a well too shallow or badly sited to be protected. That is contractor and health department territory.
Consider UV, Properly
If bacteria are recurrent rather than a one-off, ultraviolet disinfection is the standard answer — continuous protection at every tap rather than an annual round of chlorine.
Two things decide whether it works:
Specification. Use a system certified to NSF/ANSI 55 Class A, delivering 40 mJ/cm². Class B units deliver 16 mJ/cm² and are rated only for water already known to be safe, which is precisely not your situation.
Feed water. UV needs iron below 0.3 mg/L, manganese below 0.05 mg/L, hardness below 7 grains per gallon, turbidity below 1 NTU, and a 5-micron pre-filter. Above those limits the sleeve fouls, the light is blocked, and the lamp keeps glowing while delivering a fraction of its dose. Fix the feed water first, or the UV is decoration.
Afterwards, Write It Down
The date of the positive result. What you found at the wellhead. What you fixed. The date you shocked it. Both retest dates and results.
Bacteria problems recur seasonally, and the pattern is the diagnosis. An owner who can say "positive every spring after the snowmelt, clean the rest of the year" has told a contractor more than any single test ever will.
Frequently Asked Questions
Is E. coli in well water an emergency? Treat it as one. E. coli indicates fecal contamination is reaching your well, which means pathogens capable of causing serious illness may be present. Stop drinking the water immediately, use bottled or properly boiled water, and retest after treatment.
What is the difference between total coliform and E. coli? Total coliform bacteria are common in soil and surface water and indicate a pathway into your well. E. coli is a subset found specifically in the intestines of warm-blooded animals, so its presence means that pathway is carrying fecal material — a considerably more serious finding.
How do I make well water safe to drink after an E. coli result? Bring water to a rolling boil for one minute, or three minutes above 6,500 feet elevation, and use it for drinking, cooking, brushing teeth and washing produce. Bottled water is simpler. Do not rely on a standard carbon filter, which does not remove bacteria.
Can I shower with water that tested positive for E. coli? Showering and bathing are generally considered acceptable for adults with no open wounds, provided you do not swallow the water. Take care with infants and young children, who are more likely to ingest bath water, and use boiled or bottled water for brushing teeth.
What if E. coli comes back after shock chlorination? That points to an ongoing pathway rather than a one-off event — a failed well seal, a cracked casing, a nearby septic problem, or a well too shallow or poorly sited to be protected. It needs a licensed well contractor and your local health department, not another round of bleach.