🚨 If You Have a Closing Deadline
A positive coliform test will prevent a federally-backed loan (FHA, VA, USDA) from closing. Begin shock chlorination immediately and schedule a re-test for 7–14 days after treatment. Contact your lender to request a closing extension if needed. Most lenders will accommodate this when presented with documentation of active remediation.
What “Total Coliform Positive” Actually Means
Coliform bacteria are a broad group of microorganisms that include both harmless environmental bacteria and potentially dangerous pathogens. A positive total coliform result on your well test means that bacteria from that group were detected in your water sample.
The key distinction is whether E. coli was also detected:
- Total coliform positive, E. coli negative: Bacteria are present but are likely environmental in origin (soil, plant matter, insects). Still requires treatment and re-testing, but the immediate health risk is lower.
- Total coliform positive, E. coli positive: Fecal contamination is confirmed. Do not drink, cook with, or brush teeth with untreated water until a passing re-test confirms the well is clear. Use bottled water or boil all water for at least one minute.
Both results require the same treatment response. The difference is urgency and precaution in the interim.
Common Causes of a Positive Coliform Result
Before treating, it helps to understand why contamination may have occurred, because some causes require more than shock chlorination to resolve:
- Recent heavy rain or flooding — Surface water can infiltrate a poorly-sealed wellhead
- Cracked or deteriorating well casing — Allows surface water intrusion
- Inadequate wellhead seal — The well cap or seal is loose or damaged
- Nearby septic system issue — A failing drain field can contaminate groundwater
- Improper well construction — Particularly common in wells drilled before the 1970s
- Sample contamination during collection — An improperly taken sample can produce a false positive
If you cannot identify an obvious cause, a positive test on a re-check (after treatment) suggests a structural problem that requires a licensed well contractor to inspect.
Step-by-Step Response to a Positive Coliform Test
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Stop using the water for drinking and cooking if E. coli was detected
If total coliform only: use your judgment based on health vulnerability of household members (infants, elderly, immunocompromised individuals should avoid). If E. coli positive: boil water advisory applies immediately.
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Inspect the wellhead visually
Look for: a loose or cracked well cap, debris inside the casing, signs of flooding or pooled water around the wellhead, animal activity near the well, any cracks in the surface casing. Photograph everything. If structural damage is visible, call a licensed well contractor before proceeding with shock chlorination.
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Shock chlorinate the well
This is the standard remediation procedure. See our complete shock chlorination guide for exact quantities and procedure. In brief: you introduce a measured amount of unscented liquid chlorine bleach (sodium hypochlorite) into the well casing, let it sit for 12–24 hours, then flush the system thoroughly until chlorine smell is no longer detectable at the tap.
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Wait the required period before re-testing
This is where most people make the mistake of testing too soon. After shock chlorination and flushing, you must wait at least 7 days before collecting a re-test sample. Some labs and health authorities recommend 10–14 days. Testing too soon can produce a false negative (residual chlorine suppresses bacteria that return after the chlorine dissipates).
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Collect the re-test sample correctly
Use a new, lab-supplied sterile container. Follow the collection protocol exactly—incorrect collection is the most common source of both false positives and false negatives. See the sample collection guide →
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Interpret the re-test result
If the re-test is negative (no coliform detected): Your well has been successfully remediated. Provide the passing result to your lender if you’re in a real estate transaction. Continue with annual testing and monitor for recurrence.
If the re-test is still positive: Shock chlorination alone is not sufficient. You likely have a structural well issue requiring a licensed well contractor to inspect and repair the casing, seal, or grouting. -
Document everything
Keep copies of the original failing test, the shock chlorination date and procedure, and the re-test results. If this is a real estate transaction, your lender will require documentation of the full remediation process along with the passing re-test result.
When Shock Chlorination Isn’t Enough
If coliform returns after two rounds of shock chlorination, the problem is structural. Common causes:
- A crack or separation in the well casing below ground level
- Insufficient grout seal around the casing (common in older wells)
- A nearby septic system that is actively leaching into the aquifer
- The well is drawing from a shallow, naturally contaminated water table
A licensed well contractor can camera-inspect the casing and assess whether grouting, casing replacement, or deepening the well is needed. In some cases where a well is beyond repair, a new well may be the only option. Well drilling costs range from $3,500–$15,000+ depending on depth and geology.
Coliform Failure in a Real Estate Transaction
If you’re in the middle of a home purchase and the well test comes back positive for coliform:
- Notify your lender immediately. FHA, VA, and USDA loans cannot close until a passing re-test result is submitted to the underwriter.
- Request a closing extension in writing. Most lenders accommodate a 2–3 week extension when documented remediation is underway. Get the extension in writing before your current contract expires.
- Negotiate who pays for treatment. Shock chlorination is inexpensive ($50–$100 in materials). If a structural repair is needed, this is a significant negotiating point. Sellers are typically expected to deliver a well that meets water quality standards.
- Submit all documentation to your lender. Original failing test, shock chlorination record, re-test sample date, and passing result. Keep a copy for your records.
See the complete guide to closing requirements for well water →
Installing a Long-Term Disinfection System
If your well has a history of coliform positives, a long-term disinfection system is more reliable than repeated shock chlorination. Options include:
- UV disinfection system: Most effective for recurring bacterial contamination. No chemicals, no byproducts. Requires clear water (turbidity < 1 NTU). See the UV guide →
- Continuous chlorination system: Injects measured amounts of chlorine into the water supply. Effective but requires dechlorination at point of use for taste/odor.
- Point-of-use filter (NSF 58 reverse osmosis): Removes bacteria at the tap. Does not address the contamination in the well itself.