Well Disinfection for Bacterial Contamination

Well Disinfection After a Flood flyer in English and Spanish (PDF: 315 kB)

If your well water is contaminated with bacteria after a flood, you can try to disinfect the well. Well water systems may be disinfected by adding chlorine bleach (Clorox, Purex, etc.) to the water in the well. Warning: There is danger of electrical shock and damage to the well or pump if they have been flooded.

Use the following dosages as a guide:

Note: These quantities are for a well with a depth of 100 feet. Adjust the amounts according to the depth of your well. Do not use bleach with any fragrances, dyes, or additives such as scented or non- splash bleach.

• If water is cloudy, attempt to clear as much as possible by pumping the well.
• With the pump off, pour the bleach solution into the well. (Refer to the chart above). It may be necessary to lift the pump. Some wells have openings, which can be used for this purpose.
• Allow 30 minutes to let the bleach mix with the well water, then surge well by alternately starting and stopping pump in order to wash down the inside of the casing and the drop line with chlorinated water.
• If possible, use some of the heavily chlorinated water pumped from the well to wash down the inside of the well casing using a hose fastened to the faucet near the well or pressure tank.
• Open all faucets until you smell chlorine at the tap farthest from the well.
• Close the faucets and allow the mixture to stand in the system for at least 24 hours. Disinfectant contact time with bacteria is important.
• After 24 hours, turn pump on and ensure all taps and faucets are closed. Flush the chlorine mixture from the system by hooking a garden hose to an outside tap and running water until no chlorine odor is present. Since chlorine will kill grass and plants, be careful where you run the water outside.
• Do not flush the mixture into your septic system by running chlorinated water down drains! Your septic system was not designed to handle the large continuous flow of water necessary to remove the chlorine. Plus, chlorine is harmful to the beneficial bacteria that make your septic system function properly.
• Have your water tested for bacteria by a laboratory certified for bacteriological and/or chemical analysis before using it. Test water your well water regularly to ensure the safety of your water.
• If bacteria are present, do not use your well and repeat the above process until bacteria are not present.
• If the well was improperly constructed or poorly located, the contamination may not be eliminated or may be only temporarily In that case, a permanent disinfection system or a new well may be necessary.