A positive total coliform test means bacteria are getting into your well, so the well is at risk. E. coli means possible human or animal waste. Wisconsin health officials say to drink boiled, bottled or safe public water, retest, and have a licensed well driller or pump installer disinfect the well and find the cause.
Updated October 2026
Safety first: well pumps run on 230/240-volt circuits. Don’t open the pressure switch, control box or well cap wiring.
What your result means
| Result | What it means | What to do now |
|---|---|---|
| Total coliform positive, E. coli negative | The well is at risk. Bacteria are getting in somewhere. | Use boiled or bottled water for drinking and cooking. Retest. |
| E. coli positive | Possible human or animal waste in the water. | Don’t drink the water untreated. Boil it or use bottled water. Retest and have the well checked. |
| Both negative | No bacteria found in that sample. | Keep testing every year. |
Steps to take
- Switch drinking water. Boil water at a rolling boil for 1 minute, or use bottled water or a public supply with no violations.
- Retest with a certified lab to confirm the result. See where to test.
- Have the well disinfected. The DNR says disinfection is best done by a licensed well driller or pump installer, who can also inspect the wellhead.
- Retest about a week after disinfection.
- Keep using safe water until you get a clean result.
Common causes at the wellhead
You can look at the well from the outside without touching anything. Is the cap whole and snug? Is the casing at least a foot above the ground? Does water pool around it?
- Loose, cracked or missing cap. If insects or droppings get under the cap, disinfection won’t last until the seal is fixed.
- Short or buried casing. Wisconsin code requires the casing to end at least 12 inches above the ground.
- Old well pits. Pits have their own rules and often lead to replacement wells.
- Flooding. If the casing was underwater, stop drinking the water and test before using it again.
- Local geology. The Driftless area has thin soils and cracked rock, so surface water can reach wells quickly.
New in 2026: repeat failures
- Wisconsin’s well code (NR 812) was revised on March 1, 2026.
- If a well still tests positive for bacteria after 3 batch chlorinations done by a well driller or pump installer, the well must be filled and sealed by a licensed pro. See filling and sealing an old well.
- Repeated chlorination can also corrode the casing, so finding the cause matters.
- The state Well Compensation Grant covers bacteria only when the source is livestock waste or the home is in a DNR special compensation area.
When you need a licensed professional
- Disinfecting the well and inspecting the cap, casing and seal.
- Repairing or raising a damaged or short casing, or replacing a cap.
- A second positive test after disinfection.
- Deciding between a repair, a new well, or filling and sealing.
- Wisconsin rules require a DNR-licensed pump installer for pump and pressure-tank work on a drinking-water well; check with DNR if you’re unsure.
Related
- Where to test well water
- Nitrate in Driftless-area well water
- Grants and financial help for well owners
- Filling and sealing an old well
Sources
