If floodwater has covered your well, a basement, or the low corner of a lot in St. Charles, the water you see once it drops is not water you should use until it is tested. Floodwater carries silt, bacteria from soil and surfaces, and whatever chemicals it passed over. Private wells near the Missouri River tap the alluvial aquifer, so a well whose cap, casing, or pit was submerged can take in surface water. This guide covers what to check after the water recedes and the order to check it in.

Stop Using the Water First

Until a lab result says otherwise, treat the well as untested. Do not drink the water, brush teeth with it, make ice or baby formula with it, wash produce with it, or run the washer or dishwasher on it. Keep taps closed. If the pump, pressure tank, or electrical controls were under water, have a licensed well contractor inspect the system before running it. Flood debris can damage components and push material into the lines.

What a Flooded Well Test Should Cover

A standard post-flood panel usually includes the following.

  • Total coliform and E. coli bacteria. Surface water is a common source of these organisms. A positive result means the system needs disinfection and a retest, not a guess about the cause.
  • Nitrate. Runoff from fields and lawns can carry nitrate, and flooding can move it into shallow wells.
  • Metals such as iron, manganese, and lead. Flooding can stir up sediment, and disturbed well components or old plumbing can add metals.
  • Radium and uranium, if your property is in the area near the documented Weldon Spring legacy site. These are naturally occurring in the regional geology, and local concern is higher near that site. Ask the lab whether it runs radionuclide tests and whether your address falls into that area.

Visible cloudiness and sediment are useful clues, but they do not tell you whether bacteria or chemicals are present. Only a lab sample answers that.

Disinfect, Then Retest

If coliform bacteria show up, the usual sequence is shock disinfection by a qualified contractor, flushing the system, and then a retest. A single clean sample taken right after disinfection may not reflect how the system behaves once it settles. Ask the lab or your county health office how many samples to collect and how far apart to space them. Do not stop using a well that has a positive result because one later sample looks clear.

Municipal Water and Basements

If your home is on the St. Charles city supply, the water coming from the main may be unaffected by the flood, but the plumbing inside your house may not be. Flooding can damage fixtures, water heaters, and backflow devices, and it can disturb old service lines. Watch the water utility's notices for any advisory about the supply, and follow any instructions it issues. Public reports describe St. Charles tap water as hard and chlorinated, and older home plumbing can add lead risk. If your home has older plumbing, consider testing a cold tap for lead after the flood, especially if fixtures were removed or replaced.

Sump pit water, basement standing water, and floor drains are not drinking sources. Do not treat a basement sample as a substitute for a tap sample from the home.

Collecting a Usable Sample

  • Use the bottle the lab provides, and keep it closed until you are ready to fill it.
  • Follow the lab's flushing instructions for the tap, and use a cold tap unless the lab asks for something else.
  • Record the date, the water source, and that the property was flood affected.
  • Get the sample to the lab inside the time window it specifies, and keep it cool if the lab asks.

Keep the Records

Save every result, invoice, and repair note. A written history of what was tested, when, and what was done helps with insurance claims, with future buyers, and with the next round of testing. A flood is also a good reason to catch up on the routine checks you may have missed, so use the results to set your next test date while the paperwork is in front of you.