Your well tested positive for coliform. Now what?
Coliform bacteria in well water mean something has opened a path from the surface into your water, even if those bacteria are harmless themselves. An E. coli positive is more serious: DOH says it almost always signals recent fecal contamination. Stop drinking the water, use bottled or boiled water, have the cause found and the well disinfected by a professional, then retest at an accredited lab.
Street to Drainfield · updated · sources listed at the end
What does a coliform positive actually mean?
It means the water is open to contamination. DOH's coliform page explains that coliforms live in soil, on plants and in the feces of warm-blooded animals and people. They rarely cause illness, but labs test for them because they are cheap to find, and where they get in, germs that do cause illness can follow. When a lab finds total coliform, it then checks the same sample for fecal coliform or E. coli.
How is total coliform different from E. coli?
The risk level is different. DOH puts it in three tiers:
- Total coliform only: usually from soil or vegetation, and fecal contamination is unlikely, but the way in still needs finding.
- Fecal coliform: often points to recent fecal contamination, a higher risk.
- E. coli: almost always indicates recent fecal contamination, with a greater chance that pathogens are present.
An "E. coli present" result does not mean the dangerous O157:H7 strain is there, DOH says, and it probably is not. It still means human or animal waste has reached the water.
What should you drink until the well is fixed?
Bottled water, or water boiled at a rolling boil for one full minute, which DOH says destroys all forms of E. coli. DOH's Group B notice template applies that to drinking, preparing food and brushing teeth, which is sensible for any household. Thurston County's Water Lab page tells anyone whose well seems to be making them sick to stop drinking it and have it tested. The CDC adds: if a well may be contaminated, do not drink from it until it has been treated and tested.
Boiling works for bacteria only. It does nothing for chemicals, and for nitrate it can make matters worse, as our nitrate page explains.
Who disinfects the well, and how?
A licensed professional, working inside the casing. DOH publishes a procedure in Emergency Disinfection of Small Water Systems, and the county's Water Lab page carries its own steps; a licensed well driller or pump installer can carry them out. That keeps someone qualified at the open well, handling the chlorine dose, the pressure tank and the pump wiring. The DOH and Ecology owner guide notes the fix may also be treatment or a piping repair, so ask the pro to look for the cause, not just dose the well.
Where do coliform bacteria get into a well?
Usually through the top or the sides. The EPA lists rain and snowmelt washing microorganisms in, and effluent from septic drainfields reaching the water. Its well checklist covers cracked or corroded casing, broken or missing caps, and settled or cracked surface seals, and it says to slope the ground so runoff drains away from the well. With a septic system nearby, rule out a drainfield in trouble too: how a failing drainfield shows itself.
When can you retest after disinfection?
After the chlorine is gone. The county says to wait 3 to 4 days after the bleach is flushed out before collecting a coliform sample, and DOH's small-system guide says at least seven days or until no chlorine remains. Your pro or the lab will tell you which applies. The county also warns that several rounds may be needed before results come back satisfactory. Book the follow-up through private well testing.
Yours to do
- Switch to bottled or boiled water for drinking, cooking and brushing teeth.
- Look at the well cap and the ground around the casing, without opening anything.
- Keep runoff, pets and livestock away from the well head.
- Retest at an accredited lab once the pro says the chlorine is gone.
Leave to a licensed or certified pro
- Disinfecting the well by a licensed well driller or pump installer, following the DOH or county procedure.
- Repairing a casing, cap or surface seal by a licensed well driller.
- Any pump wiring by a licensed electrician; pump and tank work by a licensed pump installer.
- Septic problems near the well by a county-certified septic professional.
On the record
- 1 minuteRolling boil DOH says destroys all forms of E. coliWashington DOH
- 3–4 daysCounty wait after flushing bleach before a coliform sampleThurston County Water Lab
- 2 daysCounty lab processing time for bacteria samplesThurston County Water Lab
- Every yearDOH-recommended coliform test interval for private wellsWashington DOH
| Lab result | What DOH says it suggests | First step |
|---|---|---|
| Total coliform only | Probably environmental, from soil or plants | Find the way in; disinfect and retest |
| Fecal coliform | Often recent fecal contamination | Stop drinking; call a licensed pro |
| E. coli | Almost always recent fecal contamination | Bottled or boiled water now; disinfect and retest |
Common questions
Can I shower if the well has E. coli?
DOH's Group B notice covers drinking, food and brushing teeth. For bathing infants or anyone with a weakened immune system, ask Thurston County Environmental Health or your doctor.
Will a UV light fix a coliform problem?
The CDC lists ultraviolet treatment with pre-filtering as one way to reduce germs, and the EPA mentions UV among well disinfection options. Neither replaces finding how the bacteria got in, and a lab retest is still the proof.
Why did my well test positive right after a pump repair?
Opening the system can let bacteria in, which is why DOH and the EPA both call for a test after a well part is swapped out or fixed.
Does a coliform positive mean my septic is to blame?
Not always. Surface water, a bad cap or seal, and animal waste can all be the source. A licensed pro and the county can help narrow it down.
Sources
- Coliform Bacteria in Drinking Water, Washington DOH — total, fecal and E. coli tiers; read 6 November 2026
- Group B Coliform Bacteria, Washington DOH — one-minute rolling boil, notice advice; read 6 November 2026
- Emergency Disinfection of Small Water Systems, DOH 331-242 — DOH procedure, seven-day wait before sampling; read 6 November 2026
- Water Lab, Thurston County Environmental Health — stop drinking, 3–4 day wait, repeat rounds, two-day processing; read 6 November 2026
- Private Wells: Information for Owners, DOH 331-349 — disinfection, treatment or piping repair; read 6 November 2026
- Protect Your Home's Water, EPA — well inspection points, test after repairs; read 6 November 2026
- Potential Well Water Contaminants, EPA — runoff and drainfield effluent; read 6 November 2026
- Well Water Safety, CDC — do not drink until treated and tested; read 6 November 2026
- About Home Water Treatment Systems, CDC — UV with pre-filtering; read 6 November 2026
How this page was put together. This page draws on Washington DOH coliform and disinfection publications, the Thurston County Water Lab page, and EPA and CDC private well pages, all read on 6 November 2026. It deliberately leaves out step-by-step well chlorination: that work happens inside the casing and belongs with a licensed well driller or pump installer. The DOH and county procedures are linked for reference.
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