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Clean Flooded Wells


In a flood, private wells can be partially or fully submerged in surface water.

“As a result, the well may become contaminated with materials such as sewage, petroleum products, sediment, bacteria, viruses and other floating debris,” North Dakota State University Extension Service water quality associate Roxanne Johnson warns. “The smell of the water also could change if surface water gets into a well.”

Here is what you should do if you suspect surface water has contaminated the water you use for drinking or food preparation:

  • Boil the water for one minute to kill most types of disease-causing organisms, then let it cool and store it in clean containers with covers.
  • If you can’t boil the water, disinfect it using household chlorine bleach. Bleach will kill some, but not all, types of disease-causing organisms that may be in the water. Add 1/8 teaspoon (or eight drops) of regular, unscented liquid household chlorine bleach to each gallon of water, stir it well and let the water stand for 30 minutes before you use it. Store disinfected water in clean containers with covers.
  • If the water is cloudy, filter it through clean cloth or allow it to settle and draw off the clear water before boiling or disinfecting it.                                                                                                   

 “After the floodwaters recede, the well should be disinfected and the water tested to make sure it is safe,” says Tom Scherer, NDSU Extension agricultural engineer/water quality. “Obtain a water test kit for bacteria and nitrates from your county health department or a private certified laboratory.”

However, before disinfecting the well, you need to inspect it. Follow these inspection steps:

  • Turn off the electricity to the pump.
  • Remove accumulated debris and sediment from around the well casing.
  • If the well cap is missing or casing is damaged, call a certified well installer because large amounts of sediment and other materials may be in the well.
  • If the well cap is still on and not damaged, look inside the well for damage to the pump, piping, wires, casing, etc.

You should disinfect the well using shock chlorination if the inside of the well casing is relatively clean. The well also should be disinfected with shock chlorination after a well installer has pulled the pump and cleaned the well.

Before shock chlorinating a well, you need to make sure the only place water comes out in the house or barn is at the outside faucets and hydrants, bathtubs and sinks. Disconnect all other water appliances. Use the bypass valves on water filters, water softeners and water treatment devices. Shut off the supply valve to the water heater and drain it. If the water heater is electric, shut off the power; for a natural gas or propane water heater, shut off the fuel supply and put out the pilot light.

Then use the following steps to shock chlorinate a well:

  •  With the electricity off to the well pump, clean the well cap and outside of the casing with a solution of 1 ounce of laundry bleach in 2 gallons of clean water. Use a coarse brush.
  • Turn the electricity on and pump the well until the water is clear. Do this at the faucet or hydrant nearest to the well. Collect discharge water in a white bucket to check the water’s color and look for sediment.
  • Open each faucet in the home until the water runs clear. Then close all faucets and turn off the electricity to the pump.
  • Prepare a mixture of household bleach and water to pour down the well. You’ll need at least one 10-gallon container or two 5-gallon containers for mixing the bleach and water. Use eye protection and rubber gloves when mixing. You’ll need at least 200 parts per million of chlorine throughout the water column in the well. The amount of household bleach to achieve this depends on the diameter and depth of water in the well. If your well is 3 to 4 inches in diameter with about 50 feet of water, mix 2 quarts of bleach in 10 gallons of clean water. For a well 5 to 6 inches in diameter with 50 feet of water, mix 1 gallon of bleach in 10 gallons of clean water. If you are not sure of the amount of water in your well, double the amount of household bleach in the mixture. Household bleach is about 6 percent chlorine, so doubling the amount won’t do any harm.
  • Pour the diluted bleach solution into the well against the side of the casing. Avoid pouring directly onto the pump wiring if possible, but try to wash down the entire inside of the casing
  • Mix the chlorine throughout the water column in the well. Turn on the electricity. If possible, connect a garden hose to the nearest hydrant or faucet and place the discharge end in the top of the well. Run the water for 15 minutes. You also can mix the chlorine by starting and stopping the pump quickly several times. Let the chlorine mixture sit in the well for at least an hour.
  • Open every water outlet on the system one at a time. Run the water until you can smell chlorine, then close the faucet. Flush the toilets, refill the water heater and let the chlorine solution to remain in the system for at least four hours, although eight hours is best.
  • To purge the chlorine from the system, open all the faucets or hydrants. Start with the faucet or hydrant nearest the pressure tank and work your way to the farthest faucet or hydrant. Run each one until you can’t smell chlorine.

Now use your water test kit to obtain a water sample to test for bacteria. You should continue to use an alternative water source or boil your water until the laboratory reports the water is safe.

A safe report indicates the water does not contain E.coli and total coliform bacteria. You should have the well tested again in about two weeks to make sure the disinfection has been completely effective.

For more information, view a video at www.ag.ndsu.edu/flood/home/cleaning-up-your-home-after-flooding-video or go to www.ag.ndsu.edu/flood or www.extension.org/Floods.

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