Well Disinfection

New York State Department Of Health

Albany, NY 800-458-1158

Well Disinfection

After a well is constructed and pumped clear, or after any improvements are made, (or, if a laboratory examination of a water sample reveals bacteriological contamination) it should be disinfected with a chlorine bleach. Bleaches containing 5.25 per cent available chlorine are sold in supermarkets and grocery stores under such names as Clorox, Dazzle, Purex, White Sail, 101 etc. Here is the procedure for disinfecting a well:

1) Mix two quarts of bleach in ten gallons of water. Pour the solution into the well while it is being pumped. Keep pumping until the chlorine odor appears at all taps. Re-circulate the water back into the well for at least an hour. Then close the tap and stop the pump.

2) Mix two more quarts of bleach in ten gallons of water and pour this chlorine solution into the well. Allow the well to stand idle for at least 8 hours and preferably 12 to 24 hours.

3) Pump the well to waste, away from grass and shrubbery, through the storage tank and taps, such as an outside connection, until the odor of chlorine disappears. The chlorine may persist for 7 to 10 days depending on how much water is used.

After all the chlorine is pumped out, a water sample should be collected and tested by the health department, if this service in available, to determine whether all contamination has been eliminated. If the health department does not examine samples from private water supplies, a commercial laboratory will have to be used and prior arrangements make to pick up a sterile sample bottle and sampling instructions. Make sure all chlorine has been pumped out of well (no chlorine taste or odor in the water) before a sample is collected.

Proper disinfection of flowing wells or springs requires special treatment, which the health department will explain in specific instances.

Remember that disinfection is no assurance that water entering the well or spring is free of pollution.

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