Recommendations for Wells Affected by Flooding

If you live in an area that was recently or is currently flooded, your private well may be in danger of contamination from pollutants carried in floodwaters. If your well cap is or has been underwater, you should assume that your well is contaminated.

Find an Alternative Source of Water or Boil Your Water

If you suspect your drinking water is contaminated, your first alternative should be to obtain water from a known safe source for drinking, cooking and food preparation. You can get water from a neighbor’s well you know is safe, from a community water supply or you can purchase bottled water. If you cannot find a convenient source of safe water, you can boil your well water for five minutes before use.

If you have any questions about your well or water quality, please call the Drinking Water Program at (207) 287-2070 during business hours. For after-hour emergencies, call (207) 557-4214. Use the following procedure to disinfect your well.

Disinfecting a Well

  1. Once the water has subsided below the cap of the well, remove the well cap. Pour the appropriate amount of chlorine bleach from the table below into the well.
  2. Replace the well cap.
  3. Open all faucets, sill cocks and similar outlets individually until you smell chlorine in each outlet.
  4. Allow the mixture to stand in the system overnight, and then flush the chlorine mixture from the system using an outside faucet and garden hose. DO NOT FLUSH THE MIXTURE INTO YOUR SEPTIC SYSTEM. You may resume using the toilet facilities as the septic system is designed to handle this, but the septic system cannot handle the large amount of water needed to flush the chlorine from the well. Since the chlorine will kill grass, be careful where you run the water outside.
  5. After disinfection, the water supply should be sampled and tested for coliform bacteria to ensure that the water is safe. Sample kits for coliform bacteria are available from private and state laboratories. Sampling should be done only after the odor of chlorine disappears. It takes about 3 or 4 days of normal water usage before all of the chlorine smell disappears.


Drilled Well
(PLEASE NOTE: A greater amount of chlorine may be needed to disinfect the water depending on the degree of contamination)
50 feet
2 1/2 cups
100 feet
1 1/2 quarts
150 feet
2 quarts
200 feet
2 1/2 quarts
250 feet
3 quarts
300 feet
3 1/2 quarts


Dug Well
(Approximate amount of water in the bottom of a well and not the total depth of the well. For a surface SPRING, use 2 gallons)
Dosage (Gal)
5 feet
1/2 gallon
10 feet
1 gallon
15 feet
1 1/2 gallons
20 feet
2 gallons


For more information about coliform bacteria, click here.


Additional resources

Flooding and Your Well: Make Sure Your Drinking Water is Safe
handout in pdf format

Emergency Disinfection of Water - EPA fact sheet

Drinking Water Safety - MEMA fact sheet