Recommendations for wells inundated 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.
Boiling Your Water
If you suspect your drinking water is contaminated, you should 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
- Once the water has subsided below the cap of the well, remove the well cap. Pour the appropriate amount of chlorine bleach (Clorox, Dazzle, or other EPA/NSF approved bleach) from the table below into the well.
- Replace the well cap.
- Open all faucets, sill cocks and similar outlets individually until you smell chlorine in each outlet.
- Allow the mixture to stand in the system overnight, 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.
- After disinfection, the water supply should be sampled and tested for coliform bacteria. Sample kits for coliform bacteria are available from private and state labs. Check the yellow pages or click here for a list of certified labs. 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)
Depth |
Dosage |
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)
Depth |
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
Emergency Disinfection of Water - EPA fact sheet
Drinking Water Safety - MEMA fact sheet
