If your lab report came back positive for coliform bacteria, take a breath. A positive total-coliform result is a warning indicator, not proof that anyone is sick. It tells you that bacteria from the environment have found a way into your well, which means the path that let them in needs to be found and closed. A positive for E. coli is more serious, because E. coli signals fecal contamination, so until the water clears you should stop drinking it and switch to bottled or boiled water for drinking, cooking, brushing teeth, and making ice. The good news is that most coliform problems on Hill Country wells come from a fixable surface-level issue, not from the aquifer itself.
Total coliform versus E. coli: what each result means
Total coliform bacteria live in soil, on plants, and in surface water all across the Hill Country. They are mostly harmless on their own, which is exactly why labs test for them. They are an easy-to-detect marker. If total coliform shows up in your well, it means surface material is reaching your water somewhere, and where surface material goes, more harmful organisms can follow.
E. coli is a specific group within the coliform family that lives in the gut of warm-blooded animals. Finding it points to fecal contamination from livestock, wildlife, septic systems, or runoff, and that carries a real risk of illness. Treat any E. coli positive as a stop-drinking situation until you have a clean retest in hand.
Water trouble now, or planning ahead? Tell us what your well is doing and we will give you a straight answer and a free quote, often the same day.
Common Hill Country causes
On limestone terrain with thin soils and fractured rock, bacteria do not have far to travel to reach a wellhead. The usual culprits we find are physical, at or near the surface:
- A loose, cracked, or missing well cap. The cap is your first seal against insects, debris, and rainwater. A vented cap that has loosened or lost its screen is one of the most common entry points we see.
- Cracked, corroded, or shallow casing. If the casing has a crack, a bad joint, or does not extend far enough above grade, surface water can slip down alongside or into it instead of being held out.
- Surface water intrusion around the wellhead. Pooling water, a wellhead sitting below grade, or a poor sanitary seal lets contaminated runoff migrate straight to the borehole.
- Flooding and heavy rain. After a hard Hill Country storm or a flood, surface water can submerge a wellhead and push bacteria into the system. Many positive tests show up in the days after a big rain event.
- A nearby septic system or animal activity. Distance, soil, and the direction water moves underground all matter, and a struggling drain field uphill of the well is worth ruling out.
Shock chlorination: the standard fix
The standard first response to a coliform positive is shock chlorination, which disinfects the well, the pump, the pressure tank, and the household plumbing with a strong chlorine solution. The chlorine is mixed and circulated through the system, held in place for a number of hours so it can work, and then flushed out completely before you use the water again. Done correctly it kills the bacteria living in the well at that moment.
What shock chlorination does not do is fix the reason the bacteria got in. Think of it as cleaning the wound. If the cap is still loose or the casing is still cracked, the contamination can simply return. That is why disinfection and a physical inspection of the wellhead go together. For guidance on collecting a proper sample and reading your results, our well water testing guide walks through the process, and if your water also has an ongoing taste, odor, or mineral issue, our well water treatment guide covers longer-term options beyond a one-time shock.
Why retesting matters
Retesting is not optional, it is how you confirm the fix actually worked. After a shock chlorination, you wait until all the chlorine has flushed from the system, then collect a fresh sample and send it back to the lab. Texas testing guidance generally recommends confirming a clean result before you trust the water again, and many well owners follow up with another sample a couple of weeks later to be sure the well stays clear over time. One clean test right after chlorination is reassuring; a clean test that holds is what you are really after.
When a repeat positive means a repair, not more chlorine
Here is the key judgment call. If you shock the well, retest, and it comes back positive again, the problem is almost certainly physical. Re-chlorinating a well that keeps failing is treating the symptom while the door stays open. A repeat positive usually points to a damaged cap, compromised casing, a failed sanitary seal, or surface water still finding a way in, and that calls for a repair rather than another round of chlorine.
At that stage we inspect the wellhead, casing, and seal to locate the actual breach and correct it. That might mean replacing the cap, repairing or extending the casing, regrading around the wellhead, or sealing the system properly against surface water. Our well repair team handles exactly this kind of diagnosis, and once the well is sealed, routine well maintenance and inspections are the best way to catch a loose cap or aging seal before it turns into another positive test.
If your test came back positive and you are not sure whether you need a disinfection, a repair, or both, give us a call and we will help you read your results and figure out the right next step.