Heavy rain and river flooding can change what reaches a private well or a home plumbing system in O'Fallon. Mud, debris and standing water can get into a well casing, the pump area or the ground around the wellhead. If water pooled around your well, or your home took on floodwater, treat the water as unverified until you have tested it. This guide lays out a simple order of steps so you are not guessing.
Start With What You Can See
Before you collect any sample, look at the system. Check whether floodwater reached the well cap, the pump housing, the pressure tank, the electrical box or the controls for a softener or filter. Note any cloudiness, sediment, odor or staining in the water. Write down when the water rose, how long it stood, and whether a septic tank or drain field was covered. Those details help whoever reads your results understand what might have happened.
If you are on municipal water, the flood may not have affected the main supply, but it can still disturb a service line or plumbing inside your home. If your tap water looks, tastes or smells different, contact your water provider and ask what they are seeing in your area.
Use a Lab Designed for Private Wells
For private wells, the Missouri State Public Health Lab offers coliform, E. coli and iron-bacteria testing that is free or low cost. Ask the lab for its sample kit and written collection instructions, and follow them exactly. A lab sample is only as useful as the way it was collected, so do not substitute a sample from a jar you rinsed at home.
Steps for Collecting a Sample
- Wash your hands and use the sample bottle the lab provided. Do not open it until you are ready to fill it.
- Remove any hose, aerator or filter screen from the faucet you will use. Sanitize the faucet opening as the lab instructs.
- Choose a cold tap that draws directly from the well, ideally before any softener, filter or tank.
- Run the water to let the line clear, then fill the bottle without touching the inside of the cap or the rim.
- Label the bottle with the date, time and tap location, then deliver it to the lab promptly, keeping it cool if the instructions say so.
Decide Which Other Tests Make Sense
Bacteria testing answers the first question, but a flood can raise others. Runoff can carry nitrates, especially where shallow wells sit near fields or septic systems. If your well is deep and drawn from bedrock, ask the lab whether radium and gross alpha testing should be added, since those can occur naturally in some deep wells. Metals and general chemistry tests are available through certified labs, and the lab can help you choose the panel that fits your situation.
While You Wait for Results
Do not assume a softener, carbon filter or sediment filter removes whatever a flood can leave behind. These devices are built for specific jobs, such as reducing hardness, iron or chlorine, and they are not a general fix for contaminated water. If the lab, your local health agency or your well professional advises it, use bottled water for drinking and cooking until you have results. Keep the sample results and your notes together.
Reading Results and Choosing Next Steps
If bacteria are detected, the usual next step is professional guidance on disinfection and a retest after treatment, not a single confirmation. If nitrates or other contaminants show up, ask what source the lab or a qualified well professional thinks is responsible, and whether the well construction, casing or grading needs attention. Keep copies of every report, since they become part of your home's water history if you ever sell.
A flood is stressful, but a calm, ordered path works best: inspect, collect a proper sample, test for the right things, and act on the results you actually have. Start with the state lab's instructions and let each result guide the next decision.