When the Missouri River or a nearby creek rises over its banks, the ground around a St. Charles home can end up under floodwater. If your household runs on a private well that draws from the river-linked alluvial aquifer, that water can reach the wellhead, the surface seals, and the equipment near the ground. This guide covers what to check, what to test, and what to hold off on before you return to normal use.
Treat the water as untested
Once floodwater has covered the ground around your well or reached the well cap, treat the water as unverified until a lab result says otherwise. Do not drink it, cook with it, brush teeth with it, or give it to pets until you have results. Keep this rule even if the water looks clear and smells normal, because clear water can still carry bacteria or other substances that you cannot see or smell.
Inspect the well area before running the pump
- Confirm that the well cap or sanitary seal is still in place, intact, and seated properly.
- Look for cracks, gaps, or silt at the casing opening and the vent.
- Check whether the ground around the wellhead has washed out, softened, or collected debris.
- Look at the electrical box, pressure switch, and pump controls for water exposure or corrosion.
- Inspect the pressure tank and any exposed piping for standing water or damage.
If the electrical components sat in floodwater, shut off power at the breaker before touching them. Have a licensed professional inspect the pump and controls before restarting the system. A submerged pump that runs without a proper check can fail, and a damaged electrical component can create a hazard of its own.
Flush only after the inspection is complete
After the physical check looks sound, you can run an outside spigot or a basement tap to clear sediment from the lines. Let the water run until it looks clear, and keep the discharge away from the wellhead and any drainage paths. Running water does not make it safe to drink. It only moves the sediment out of the pipes so that your test sample reflects the water the well is actually producing.
Get a lab test, not just a visual check
A flood check should include a laboratory test from a certified lab. At a minimum, ask for a coliform and E. coli test, which show whether surface water has entered the well. Because floodwater moves material across the land, it is also a good time to ask about nitrate, pH, iron, manganese, and hardness. Some groundwater in the area also contains naturally occurring radium and uranium, so ask the lab whether radionuclide testing makes sense for your property.
Follow the lab's collection instructions exactly. Use the bottle they provide, avoid touching the inside of the cap, and ship or deliver the sample within the time window they specify. A sample collected incorrectly can give you a result that does not describe your water, which can lead to the wrong next step.
Disinfection after a flood
Many homeowners ask about shock disinfection of a well after flooding. The method, the amount of disinfectant, and the contact time depend on the well's construction, depth, and water volume. Those details should come from the lab, your county health department, or a licensed well professional, not from a general rule. Do not guess at amounts. After any disinfection, retest the water as the lab or health department recommends, and keep the water off limits until the results come back clean.
If you are on city water in St. Charles
Homes in St. Charles that are connected to the city system are supplied by a utility rather than a private well. Flooding can still affect water service, pressure, and treatment, so watch for any boil advisory or notice from the utility. If one is issued, follow it fully, even if your tap water looks normal. Do not rely on your own filter to make untested water safe during an advisory.
Watch for changes in the weeks after
Some problems show up after the water has settled. Keep a simple log with dates and observations so you can compare results over time.
- Cloudiness, sediment, or grit in the tap water that does not clear.
- A new odor, especially a rotten-egg or chemical smell that was not present before.
- Changes in pressure, pump cycling, or the sound of the pump running longer than usual.
- New staining on sinks, tubs, toilets, or laundry, which can point to iron or manganese.
- A taste that differs from your usual water, even when the lab results look acceptable.
Any of these signs is a reason to retest, not a diagnosis. Share the lab results and your log with whoever helps you plan the next step, whether that is a follow-up test or a review of your equipment.
Keep records for the next flood
Save every lab report, inspection note, and photo of the wellhead. A clear record of the well's condition before and after a flood makes the next check faster and easier. It also helps you spot slow changes that a single test would miss, such as a seal that has loosened over several seasons or a pump that has started to work harder than it did before.