What to do with your well after a flood

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Assume the water is contaminated.

The Minnesota Department of Health says that if a well floods, you should assume it's contaminated. The EPA warns that drinking or washing with water from a flooded well can make you sick. Minnesota adds brushing your teeth and cooking to that list.

Use bottled water until the well has been disinfected and a lab test comes back clean.

The EPA says wells more than 10 years old or less than 50 feet deep are likely to be contaminated after a flood, even if you can't see any damage.

Leave the pump off until the wiring is checked.

The EPA's first warning is in capital letters: don't turn on the pump. A flooded pump or control box can shock you and can damage the well. Rubber boots and gloves won't protect you.

Wait until the water has gone down and everything has dried. Then have a qualified electrician, well contractor or pump contractor check the wiring before the power goes back on. The EPA says pumps that took in silt and sand need cleaning, or they can burn out.

Have the well itself checked if water went over it.

Fast flood water can carry debris that loosens the cap, bends the casing or knocks parts out of place. Sediment can get inside if the cap wasn't tight. Minnesota says that if flood water covered or entered the well, a licensed contractor should inspect it, clean out any sediment and disinfect it. Don't run the pump to clear the mud yourself. Minnesota warns that can ruin the pump.

The EPA says drilled, driven and bored wells are best disinfected by a well or pump contractor, because they're hard for an owner to disinfect thoroughly.

Disinfect the well once it's safe to run.

Here's the EPA's emergency procedure for a flooded well, in short:

1. If the water is muddy or cloudy, run an outside hose until it runs clear. (If flood water went into the well, leave the sediment cleanup to a contractor.)
2. Pour 1 gallon of plain unscented bleach into the well casing through the vent or plug opening. For a dug or bored well, lift off the cover.
3. Run water from an outside hose back into the casing until you smell chlorine at the hose.
4. Switch any treatment system to bypass. Open every cold water faucet, inside and outside, until you smell chlorine, then shut them off.
5. Wait 6 to 24 hours. Don't drink, cook, bathe or wash with the water during this time.
6. Run an outside hose until the chlorine smell is gone. Aim it where it won't harm plants, streams, lakes or the septic system.

Our shock chlorination guide has more detail and a way to work out the bleach amount for your well size.

Test for bacteria 7 to 10 days later, then keep testing.

The EPA says to test for bacteria 7 to 10 days after disinfecting. Your local health department may test it for you, or it can point you to a certified lab.

One clean test isn't the end of it. The EPA says a flooded well may not be a reliable water source for many months, because flood water keeps moving through the ground and failing septic systems can keep leaking. Minnesota says you may need to disinfect and test several times before the bacteria are gone.

Chlorine only deals with germs. The EPA notes that disinfection won't protect you from pesticides, heavy metals or other chemicals. If fuel tanks, farm chemicals or drums washed near your well, ask your health department what else to test for.

Don't use the septic system right away.

The EPA says septic systems shouldn't be used right after a flood. Drain fields won't work until the ground water goes down, and septic lines may have broken.

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