When to Disinfect

All newly constructed and existing water supplies which have been replaced, reconstructed, flooded, or reactivated after a period of shutdown must be disinfected to guarantee a safe drinking water supply.


What to Use

Sodium hypochlorite or liquid laundry bleach (3 percent or 5.25 percent chlorine); unscented.

The solution – Make a five gallon batch:

  • two gallons 3 percent laundry bleach in three gallons water
  • one gallon 5.25 percent laundry bleach in four gallons water


The Procedure

  1. Stop pump. Remove well cap, vent pipe, or plug if well is equipped with a sanitary well seal.
  2. Small wells (12″ or smaller diameter): use half of prepared solution. Large wells: use entire five gallon batch.
  3. Start pump. Connect a hose to a house spigot and run water directly into the well. Continue until chlorine odor is present in the water running from the hose. Run water for 15 minutes.
  4. Shut off water supply to hose. Open all taps (include all cold and hot water valves, remember basement fixtures). Allow water to run until each tap has a distinct chlorine odor. Close taps. Stop pump. Add remainder of solution to well or a second batch if large well.
  5. Allow to stand for 12 to 24 hours. The retention time of the solution is crucial for the disinfection process.
  6. Start pump. Open all taps. Allow water to run until chlorine odor disappears.
  7. Request your local health department to collect samples and approve your water before using.



For more information, call the Water Quality Division at 513.946.7966 or visit


Download a printable version of this fact sheet here.


250 William Howard Taft Road
2nd Floor, Cincinnati, OH 45219
Phone 513.946.7800 Fax 513.946.7890