A coliform result on a private well is one of the more unsettling lines a homeowner can receive from a lab. In O'Fallon, where many homes draw from shallow or poorly sealed wells that are more exposed to surface influence, it helps to know what the result means and what to do in the days that follow. This guide walks through the first week in order.
What the result is saying
Total coliform is a broad group of bacteria. Finding them in a sample is an indicator that the well may have a route for surface water or soil to get in, such as a cracked casing, a loose cap, a damaged seal, or a nearby failing septic system. E. coli is a more specific member of that group that points to recent contamination from animal or human waste. A positive total coliform result with no E. coli is still a reason to act, but it is not the same finding as confirmed fecal contamination. Read the report carefully to see which organism was found.
Step 1: Stop drinking the water untreated
Until a retest comes back clean, use water from a source you know is suitable for drinking, cooking, brushing teeth, and any other use the lab or health department recommends. Boiling water until it reaches a rolling boil, then letting it cool before storing it, is a common interim measure for bacteria. Boiling does not remove chemicals or nitrates, so treat it as a short-term step for bacteria only.
Step 2: Retest before deciding anything else
A single result can come from a sampling mistake, a dirty faucet, or a sample taken from the wrong tap. Ask the MO State Public Health Lab about its free or low-cost coliform and E. coli testing, and follow the collection instructions exactly. Sample from a tap close to the wellhead that is not connected to a softener, filter, or other treatment, and disinfect the faucet as the lab directs. Pay attention to the hold time and shipping rules on the lab form, because a sample that sits too long can give a misleading result.
Step 3: Inspect the well for an entry point
Most positive results trace back to something physical. Work from the top down.
- Check the well cap or vent screen for cracks, missing gaskets, or insects and debris inside.
- Look at the top of the casing for gaps, rust holes, or a pulled-away seal where pipes enter.
- Walk the ground around the wellhead. Standing water, low spots, or soil that slopes toward the casing all matter.
- Note the distance from the well to any septic tank, drain field, animal lot, or fertilized area. Sketch it on paper so you can compare it with the lab results later.
- Check the pressure tank and exposed pipes for recent repairs or open fittings that may have let in contamination during service.
Step 4: Consider what changed recently
Write down any recent pump work, well repair, new fixtures, flooding, storm runoff, or digging near the septic field. Contamination often follows a disturbance. If the well was recently serviced, ask the person who did the work what disinfection was performed and whether the system was tested afterward.
Step 5: Disinfect only after the entry point is fixed
Shock chlorination is a common response to a confirmed bacterial result, but it does not fix a well that still has an open route for contamination. Disinfecting while the cap is cracked or the casing is open invites a repeat result. Repair the physical problem first, then disinfect, then retest. Several retests spaced apart are typical before a well is considered clear. Whoever performs the disinfection should follow state and lab guidance and keep a written record of the dose, the contact time, and the flushing steps.
Step 6: Keep a running record
Keep copies of each lab report, dates of inspections and repairs, photos of the wellhead, and notes on what you changed. A clear sequence of results helps a repair person or the lab interpret what is happening, and it shows whether the problem is returning. If you rent your O'Fallon home, send the report to your landlord in writing and keep a copy for yourself.
When to get outside help
Call a licensed well contractor if the cap, casing, or pitless adapter needs repair, if the well's construction records are unclear, or if results keep coming back positive after the entry point has been addressed. The local health department and the MO State Public Health Lab can tell you which steps they recommend for your situation. A qualified professional can confirm whether the well needs to be sealed differently, relocated, or deepened, but start with the simplest checks first.
The first week is mostly about limiting exposure, confirming the result, and finding the cause. Once you know where the water is getting in, the rest of the plan usually becomes clear.