When the Missouri River climbs over its banks, the effects do not stop at the shoreline. In St. Charles, many homes outside the municipal system draw from private wells that tap the Missouri River alluvial aquifer, a layer of sand and gravel that sits close to the river and responds quickly to flooding. If your well is in low ground, or the water rose higher than you have seen before, treat the water as untested until you have a lab report in hand.

Why a river rise can reach your well

A well is designed to draw from deep water, but the top of the casing and the area around it are exposed to the surface. When floodwater stands over the wellhead, it can enter through a cracked or missing cap, a loose vent screen, a damaged seal, or an open pit. Floodwater carries silt, organic material, bacteria from runoff, and chemicals washed off fields and yards. Even a well that has never had a problem can take on surface water during a flood.

Steps to take before anyone drinks the water

  • Keep the tap off for drinking, cooking, brushing teeth, and making ice until a lab result comes back clean.
  • Use water from a source you already know is safe, such as sealed bottled water, for drinking and food preparation in the meantime.
  • Photograph the wellhead, cap, and surrounding ground, and note the height of any mud line on the casing. These photos help a technician and a health office understand what happened.
  • Write down the date the water went over the wellhead and the date it drained.

Check the well and its electrical parts

Look at the cap, vent, and any buried or ground-level access points for silt, debris, or standing water. If the pump control box, wiring, or pressure switch was under water, shut off power at the breaker and have a licensed electrician or well contractor inspect it before you restore power. Water in electrical components is a safety issue apart from the water quality question. Do not run the pump to test it while the ground around the wellhead is still saturated.

Flushing and disinfection

Once the area has drained, a qualified well contractor can disinfect the well and the system, usually by adding a measured dose of chlorine and circulating it through the pipes before flushing. Only a professional should set the dose, since the right amount depends on the well depth, casing, and system. After disinfection, run an outdoor hose bib away from the house until the water runs clear. Clear water is not proof of safety, so the lab test still decides when the water is ready to use.

Testing the water

Ask a state-certified laboratory for a kit that covers the basic items a flooded well needs checked. A typical post-flood panel includes:

  • Total coliform and E. coli, the most direct check for surface-water bacteria
  • Nitrate, since runoff from fields and lawns can carry it into shallow water
  • General chemistry, including iron, manganese, hardness, and pH, which can shift when silt disturbs the aquifer
  • Radium or uranium, if your property is in an area where these occur naturally, including the area near the documented Weldon Spring legacy site

Follow the lab's sampling instructions closely, including the bottle type, the timing, and the chain of custody form. Ask the lab how long results take. If you have an older test on file, compare the new results against it so you can see what changed.

Living with the water while you wait

Lab results can take days, and the water may look fine the whole time. Keep using stored or bottled water for drinking and cooking until the results are back and you understand them. If the water later turns cloudy, smells strange, or changes color, stop using it and retest. Sediment in the water may settle over several weeks, so run a faucet and check for grit after the system has stabilized.

When to call for help

Contact a licensed well contractor if the wellhead was damaged, the pump or electrical system was submerged, or the lab finds bacteria or any contaminant above the limits on the report. Your local health department can explain the results and the next steps for your household. Keep every test report, receipt, and photo together in one folder. If you sell or refinance the home later, that record will show a buyer or lender exactly what happened and how it was handled.