Check, disinfect flooded wells

If your well has been flooded, the well and entire water system should be cleaned and disinfected. Floods can contaminate wells with silt, raw sewage, oil and disease organisms.

First, remove silt and debris from the well and examine the casing, motors and pumps, piping, electrical and other system components for damage. Consult a serviceman if damage is extensive or if you are unable to make repairs.

To disinfect a well:

Pump the water until it is clear.
Scrub and disinfect the pump room and wash all equipment with at least a 2 percent chlorine solution. Note: Laundry bleach is usually 5 percent chlorine, so mix 1 gallon with 1 1/2 gallons of water.
Remove the well seal or plug at the top of the casing. Pour a solution of one quart of laundry bleach and 3 gallons of water into the top of the casing. Leave it there at least fours hours, preferably overnight.
Pump the chlorinated water through the system. While filling all piping, open one faucet at a time until there is a strong chlorine odor at each faucet. Close the faucet and leave the chlorine in the piping at least two hours, preferably overnight.
Pump and flush the system until the taste and odor of chlorine are no longer present.
Have the water tested. Boil or treat all drinking water until the water test indicates the water is safe for all purposes.

To disinfect a cistern:

First, pump it dry using an auxiliary pump. Do not pump water through the piping system.
After pumping dry, wash the walls, ceiling and floor with clean water and pump out the dirty water.
Next, check the cistern walls, ceiling and floor for cracks where ground water could come in.
Disinfect the cistern's interior using a solution of 1 quart of liquid household bleach to 3 gallons of water. The chlorine solution can be applied using a sprayer or scrubbing with a stiff broom. Pump out the disinfecting solution that collects in the bottom of the cistern.
Decontaminate the piping system before using it. Disinfect, using the same procedure for wells.
Fill cistern with water for use and have it tested. The water should have a chlorine taste for a while, but it should be safe. Drinking water should be treated and boiled until the water is tested and found safe for drinking.

Further reading: MU Extension publication WQ102 Bacteria in Drinking Water http://extension.missouri.edu/xplor/envqual/wq0102.htm

For more information, contact the University of Missouri Extension center in your county, or call 573-882-7477.

Eric Evans
Emergency Management Specialist
Fire and Rescue Training Institute.
University of Missouri Extension

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Reviewed 12/12/07