A positive coliform test on your well water is not a reason to panic. It is a reason to stop drinking the water until you know what you are dealing with.
Most families who get this result come to us having already dug through search results and ended up more confused than when they started. So here is the plain version: coliform bacteria in your well water means something got in that should not have. The question is where and how. That answer changes everything about what you do next.
What coliform actually means
Coliform bacteria are common in the natural environment. They live in soil, in plant matter, in animal and human waste. Finding them in your water does not automatically mean someone is about to get sick. But it does mean the barrier between surface conditions and your water column has failed somewhere.
Total coliform is the broad category. A positive result here tells you there is a contamination pathway. E. coli is fecal coliform, meaning direct animal or human waste is reaching your water. If your test came back positive for E. coli specifically, that moves faster and should be treated as urgent.
We covered what different test results mean in detail in our piece on arsenic, nitrates, and coliform in Texas well water. This piece is about what to do after that result is in your hand.
Stop drinking the water first
Use bottled water for drinking and cooking until the well has been treated and a clean retest comes back. Do not use tap water for infants, pregnant women, or anyone with a weakened immune system during this window.
You can typically still use well water for irrigating outdoors, flushing toilets, and washing laundry. But for anything that goes in the mouth, use bottled water until the retest clears.
Figure out where it came from
This is where most advice falls short. It tells you to shock chlorinate the well and retest. That is part of the process. But shocking the well without finding the contamination pathway often means bacteria come back weeks later when the next hard rain hits. That pattern is common enough that we wrote it up separately as bacteria in well water after rain.
Common sources of coliform intrusion:
- A cracked or degraded wellhead seal that lets surface water wash in during rain
- A damaged or missing casing cap
- Casing that has corroded or cracked below grade
- Improper grouting where the casing meets the surface
- A septic system too close to the well, or with a failing lateral field
- Agricultural runoff reaching the water table
At J4 Water Works we look at the wellhead first. Surface seal issues are the most common cause and often the least expensive to fix. If the cap is missing or cracked, rain carries surface bacteria down the outside of the casing into your water. A visual inspection finds that before anything else happens.
Shock chlorination: what it does
Shock chlorination means running a measured dose of chlorine into the well casing, letting it circulate through the system, and then flushing it out completely before retesting. Done correctly, it kills bacteria present in the water column and along the casing walls.
A few things matter here. The concentration has to be right for the well's volume. Contact time matters. Flushing chlorinated water completely from every line in the house before you retest matters. Chlorine residue in the sample suppresses bacteria on the test even if the source problem is still there. A clean test on a system still carrying treatment chemicals is not a clean test.
We run the chlorination process and advise on when to pull the retest sample so you are not wasting time on a result you cannot trust.
What to do if it comes back positive again
If the retest is clean, return to using the water and keep the test records on file. If the retest is still positive, the source of intrusion has not been addressed. Shocking clears bacteria present at that moment. It does not seal a cracked casing or fix a degraded grout collar.
We have come out to wells that had been shocked two and three times with repeated positive retests. In each case, no one had physically looked at the casing seal. Every rainstorm was washing bacteria back in through the same opening. Finding the source stops the cycle. Repeated shocking without finding the source does not.
When the source is the casing itself
A failing grouting seal at the surface can often be repaired without replacing the entire casing. We excavate around the top of the casing, clean the area, and regrout. If the casing has corroded or cracked below grade, that is a more involved repair. Sometimes a liner can be placed inside the existing casing. Sometimes the well needs to be re-drilled.
Our starting point is always looking at what is wrong before we talk about replacement. We diagnose before we quote. Most of the time the fix is less involved than the homeowner feared walking in.
Testing going forward
A clean retest after treatment does not mean you stop testing. A well that has had a positive coliform result should be retested for bacteria annually at minimum. After a heavy rainfall event, an additional test is worth running, because surface intrusion events often follow storms. Our piece on how often to test your well water covers the full schedule.
If ongoing contamination cannot be resolved at the source, a UV disinfection system or a point-of-use unit is worth discussing as part of a broader treatment plan, but that is a backstop rather than a fix.
If the water is not right, nothing else on the land works. A coliform result tells you something changed. Find it, fix it, verify the fix. That is the right order. We show up, we explain it, we get it done.