Positive Coliform Test: What to Do
A positive total coliform or E. coli result on a private well: what it means, what to do today, and how to clear the well.
What the result means
Total coliform bacteria are an indicator: they show that surface water or soil is getting into the water supply. E. coli is the stronger warning, since it comes from human or animal waste. EPA recommends testing a private well for total coliform every year, and again after flooding or repairs.
Today
- Stop drinking the tap water; use bottled water, or boil water for one minute, for drinking, cooking, formula and brushing teeth.
- Look for the cause: a loose or cracked well cap, flood water over the wellhead, recent pump work, or a septic system nearby.
- Call your county health department; most can explain the result and the retest.
Clear the well
Shock chlorination by a licensed well contractor or a careful owner following county instructions disinfects the well and plumbing. Flush the chlorine out, wait as the county directs, then retest. Wake County, for example, sells a coliform retest for $25 through its well program. Florida DOH says county health departments usually charge $20 to $30 per bacteria sample.
If it keeps coming back
Repeat positives mean a structural problem: fix the cap, grout or casing first. If the well cannot be sealed, a UV disinfection unit at the end of the treatment train is the usual answer; HomeGuide lists UV systems at $700 to $2,500 installed (cited as text). UV needs clear water, so sediment and iron filters go ahead of it.
Sources
EPA, Protect your home's water; Florida DOH, Private well water testing; Wake County, Well water testing; HomeGuide, Well Water Filtration System Cost (Apr 24, 2026, cited as text).
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