If you draw your water from a private well in St. Charles, a bacteria test is one of the most useful checks you can run. Coliform bacteria are a broad group that testers use as an indicator. A positive result means surface water or shallow infiltration may have reached the well. That is a reason to look at the well setup and retest, not a diagnosis of anything in your home.
Why your own test matters
Private wells in and around St. Charles tap the Missouri River alluvial aquifer, and water can move through gravel and sand from the surface more quickly than it does through deep bedrock. Public water reports for the city describe a different supply, so they cannot tell you what is in your well. Only a sample from your own well answers that question.
Before you collect the sample
- Call a certified lab that accepts drinking water samples for bacteria. Ask which bottle they supply, whether it contains a preservative, and how quickly the sample must reach them.
- Pick a dry weekday when you can deliver the sample the same day. Avoid holidays and weekends unless the lab confirms it will accept samples then.
- Do not rinse the sterile bottle or touch the inside of the cap. Keep the lid on until the moment you fill it.
- Wash your hands before you start, and keep the bottle away from the faucet spout and your fingers.
Collecting the sample
- Remove the aerator from the faucet you will use. Choose a cold tap close to the well, ideally before any filter, softener or other treatment, so you test the raw water.
- Wipe the faucet outlet with alcohol and let it air dry. Then run the cold water for several minutes so the line clears.
- Fill the bottle to the marked line without letting the spout touch the bottle. Cap it right away.
- Label the bottle with your name, address, date, time and sample location, and fill out the lab form completely.
- Keep the sample cool and out of direct sun until you deliver it, following the lab's instructions for shipping or drop-off.
Reading the result
Most labs report bacteria as present or absent for each sample. An absent result is a good sign for that day and that sample, but it does not prove the well will stay clean. Water quality can change after rain, flooding, pump work or changes in the water level, so testing on a schedule matters.
If the result is present, retest the well before you change anything. A single sample can be affected by a dirty bottle, a dirty faucet or a sampling mistake. If the second result is also present, the next step is to inspect the well. Check the well cap for cracks and gaps, the vent screen for blockage or damage, and the ground around the wellhead for low spots that hold water. Grading the ground so water runs away from the well is a common fix.
Disinfecting a well is a job for a qualified professional who knows your well construction. A simple shock treatment without a follow-up test can leave you with a false sense of security, so plan to retest after any treatment and after the water has been flushed as directed.
What a bacteria test does not cover
A coliform test does not measure nitrate, metals, hardness, radium or uranium. Those need their own tests. Nitrate is worth checking if you live near fields or livestock. Radium and uranium are worth checking in areas with known natural or legacy sources, and the area around the Weldon Spring site is one such area. Ask the lab which panels they offer and what each one measures.
A simple routine
Test your well at least once a year, and again after any flood, well repair, or sudden change in taste, smell or color. Keep every report in one folder with the date and sample location. Over time, those records show whether your well is stable or changing, and they help any future inspector or service person understand your water.