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 is 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 made to pick up a sterile sample bottle and sampling instructions. 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.
Chlorine is toxic.
Obey all safety precautions. Bleach sold in supermarkets may not be Food Grade. Public Water Systems must use NSF approved chemicals. In an emergency, contaminated well water or surface water can be made satisfactory for drinking by boiling or by chemical disinfection. Filtering the water through a clean cloth or milk strainer may help.