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Well Water Safety

Disinfecting Your Well (Dug & Bored Well)

Shocking is a temporary method of disinfection used to eliminate a one time case of bacterial contamination. Shocking should not be used routinely or repeatedly. It is not a substitute for eliminating an ongoing source of contamination or a defect in your well.

Shock chlorination involves adding large amounts of chlorine to the water in the well and pumping it through the system. The chlorinated water is left in the system long enough to ensure complete disinfection.

Dug & Bored Well Disinfection

To disinfect the water in your well, you will need to shock chlorinate the system with a concentration of plain bleach (5.25% sodium hypochlorite) at approximately 250 mg/L. The following chart will assist you in determining the amount of chlorine to add to your well.

Chlorine required for dug and bored wells casing diameter 0.9 meters or 3 feet

Water Depth
Meters

Water Depth
Feet

Household Bleach 5.25%
Litres

Household Bleach 5.25%
Quarts

1.5

5

1.1

1

3.0

10

2.2

2

4.5

15

3.3

3

6.0

20

4.4

4

7.5

25

5.5

5

9.0

30

6.6

6

10.5

35

7.7

7

12

40

8.8

8

(Note: All Conversions Are Approximate)

Note: Be careful when handling bleach solutions. It is recommended you wear rubber gloves, goggles, and a protective apron. If chlorine accidentally gets on your skin you should immediately flush your skin with clean water.

Never mix chlorine with other cleaning agents because toxic gases may be formed. Regular household bleach (Sodium Hypochlorite 5.25%) must be used to chlorinate your well. Do not use "fresh scent" bleach or other products to disinfect wells.


  1. Prior to chlorinating your well, ensure that you obtain a sufficient amount of potable drinking water to last over the period of time it takes to disinfect the well. Disinfected well water or alternative potable water is recommended.

  1. Disconnect carbon or charcoal filters. Other treatment devices including water softeners, iron filters and sand filters should be chlorinated. Check first with the manufacturer's literature to ensure that chlorine will not damage the treatment equipment.

  1. Using the chart as a reference, determine the amount of chlorine to disinfect the volume of water in your well.

  1. Mix the appropriate amount of chlorine with water before applying it to the well. Mixing of the chlorine solution can be performed using a ratio of 1 unit volume of bleach to 10 units of water (e.g. 1 litre of bleach for every 10 litres of water). This procedure can be performed using a large, clean and sanitary container. Add the chlorine through the top of dug or bored well by removing the lid and splash the disinfectant mixture around the wall or lining of the well and ensure that the solution contacts all parts of the well casing.

  1. Turn on all faucets to distribute chlorinated water throughout the plumbing system until you can smell chlorine. You can turn off the heating element on your hot water heater to save energy during this process.

  1. Let the water remain in the system for 12 to 24 hours.

  1. Flush the system of remaining chlorine. Do not drain chlorinated water into your septic system. Do not discharge the water to a stream or pond. Connect a hose to an outside tap and drain the water onto a remote location on the property away from the septic system and well. Once the smell of chlorine dissipates you may turn on the indoor faucets until the smell of chlorine is completely removed.

  1. Wait one (1) week before collecting a water sample for bacteriological testing so that all traces of chlorine have been flushed from the system.

If shock chlorination treatment does not eliminate the bacteriological problem or you experience chronic contamination in your well, the Health Department suggests you consider a water treatment device.

For more information please refer to the Homeowners Well Maintenance Checklist (PDF)