It may be necessary to disinfect your well if bacteria tests show that it has become contaminated or if your well was impacted by flood waters. After flood waters recede or you have taken steps to prevent contamination, the bacteria that have already entered into it can cause ongoing water quality problems. Problems which can result from bacterial contamination of a well include an increased risk of illness and the production of unpleasant tastes and odors.

The method outlined below describes a general procedure to disinfect your well. If you have any questions about this procedure contact an Environmental Health Officer for advice.

Pour unscented household bleach (5 percent chlorine) directly into the well. Make sure that the chlorine gets all the way to the bottom of the well. (Please note: this instruction applies to all types of wells, be they drilled, driven or dug. In every case, pour the chlorine solution right down into the well, either through the drillpipe, or well head, or simply by adding the bleach to the water in an open or dug well, preferably through a hose inserted to the bottom of the well.) Check the amount of chlorine to add in the chart that follows.

• Start the pump and open all taps.
• Close the taps and stop the pump when you begin to smell chlorine at the taps.
• Open the valve or plug at the top of the pressure tank just before stopping the pump to allow the solution to contact the entire inside surface of the tank. Then close the valve or plug.
• Leave the chlorine water in the system for 24 hours. This is a very strong chlorine solution (about what you should use for cleaning floors) – DO NOT DRINK THE WATER
• Pump out the water until the chlorine odour disappears.
• Do not drain this water into a stream, ditch or storm drain which connects with any fish-bearing streams.
• Monitor frequently and treat again as necessary.
• Control the factors that limit the effect of chlorine, e.g. cloudiness, and high levels of iron, manganese and hydrogen sulphide.
  
  

Amount of Bleach Solution Required to Disinfect Water Systems

Example:

1.        Depth to bottom of well (A) = 90 ft (27 m)

2.        Depth to water in well (B) = 20 ft (6 m)

3.        Water column (A – B) =  90 ft – 20 ft = 70 ft (21 m)

4.        Well diameter = 6 inch (150 mm)

5.        From table, use 10 tsp (50 mL) of bleach to disinfect each 10 ft (3 m) of water column

6.        Multiplier =   water column
                         10 ft (3 m)
        =  70 ft (21 m)
              10 ft (3 m)
        =  7.0

7.        Volume of bleach = Value in table (step 5) × Multiplier (step 6) = 10 tsp (50 mL) × 7.0 = 70 tsp (350 mL) 
        … about 1½  cups

Add 1½  cups (350 mL) bleach to your well and follow the rest of the steps: 

· Start the pump and open all taps …