How to Fix Coliform in Well Water

The well cap must be secure.
The well cap must be secure. (Image: Jupiterimages/ Images)

By itself, coliform bacteria found in well water pose little risk to humans. They are commonly found in waste-related water such as sewage, livestock waste and other runoff containing illness-causing bacteria, such as diarrhea, salmonellosis, hepatitis or shigellosis. As the bacteria seep into the ground, the ground filters them. Testing for every organism is expensive and time-consuming, so labs initially test for coliforms. If you need to trace all contaminants, you’ll need a full lab test. If tests indicate coliforms in your well, it has a defect allowing ground-level contamination.

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Check your well cap. The cap must fit tightly to prevent dust, bugs, waste water and other contaminants from entering the well. Improvising by stuffing rags into the casing or putting a can on top of the cap does not secure the well.

Turn vented caps so the vents face toward the ground. This helps prevent dust and debris from settling in the cap. Install a screen to block insects and small rodents.

Install a tight seal around the pump wiring where it enters the well casing. Bacteria can enter the tiniest openings.

Pour a nonporous slurry of clay or concrete around the outside of the well casing. A well borehole is typically larger than the casing to make installation easier. Contaminants eventually seep into the well through the exterior if it’s left unprotected.

Use landscaping to divert the waste water or livestock runoff that is causing the problem.

Inspect the well for signs of holes or cracks in the casing. Older wells constructed with brick or concrete tile are prone to these problems. Once a crack forms, contaminants easily enter the well. If the damage is near the top of the well, you may be able to fix it. Repairing a steel casing is more difficult. A new well might be a better investment.

Replace the well or move it. If your well is old, a full replacement might be the quickest, most effective and least expensive option.

Install EPA-approved and NSF-certified continuous disinfection equipment. There are four types: chlorinator, chemical feed, ultraviolet purifier or ozonation. Check with your local health department before you buy a system.

Tips & Warnings

  • After repairing a well, sanitize the well and plumbing with chlorine in a process commonly known as “shock chlorinating.” Submit new water samples for testing after the chlorine dissipates.


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