How to shock/disinfect a well with a hot water tank*

* Hot water on demand (tankless) systems must be handled differently to avoid damaging the heat exchanger, seals or sensors. (See below for guidance.)

Well owners can disinfect their own well themselves but care must be taken to shock/disinfect a well safely and effectively. Consult or hire a registered well driller, registered pump installer or qualified professional if unsure.

Step 1: First look for potential sources of contamination
Before disinfecting the well an inspection should be done to look for:

• Are there any potential sewage contamination sources near the well, e.g., manure or compost piles, septic fields?
• Is the ground sloping away from the well at the wellhead to promote drainage and avoid ponding?
• Is the well cap missing, cracked or damaged? Does the well cap allow for water or vermin to enter the well?
• Is the well casing stickup less than 1 foot above the ground surface? Can surface or standing water easily flood over the top of the well casing?
• Does the well have a surface seal, e.g., is there a space or gap between the well casing and the ground around the well? If there is a surface seal are there noticeable cracks in the surface seal around the well casing?

If the inspection identifies a “Yes” to any of the above questions, the problem should be fixed before disinfecting the well. Otherwise the well will continue to be vulnerable to contamination.

A qualified well driller or pump installer must be hired to repair or install a surface seal for a well or to add casing to increase the well stickup. After this work is completed, it is a requirement that the qualified well driller or pump installer promptly disinfect the well.

Step 2. Preparation
Notify all users of the well not to drink the water or bathe in it while the strong solution of chlorine is present in the system. Store sufficient water for use during a 12 hour period.

For the specific procedure, follow the information in the provincial brochure). Follow the recommended guidelines as over chlorination can have a negative effect on the disinfection process. In general terms, the following steps will be taken.

Step 3. Determine volume of water in the well and the pH of the well water

Step 4: Mix the bleach solution.

Step 5: Add the chlorine mixture to the well

Step 6: Circulate chlorinated water

Step 7: Disinfect the plumbing system

Step 8: Flush chlorine solution out of the well and distribution system

Step 9: Test your water

Wait 7–10 days, then collect a bacteria test sample.

Do not assume the well is safe without a follow-up test and don’t drink the water without boiling it until the test results show it is safe to drink.

Retest again in one month after disinfection to ensure the water is potable.

How to shock/disinfect a well with a tankless (hot water on demand) system

If your manufacturer has specific instructions, those always override any of the following instructions.
Follow the same steps as provided for a system with a hot water tank with the following exceptions.
Before you start (important)
1. Turn OFF power
2. Close isolation valves to the heater if installed.
3. Remove or bypass filters, softeners, reverse osmosis systems.
Add chlorine to the system
Distribute chlorinated water
Flush the system
After chlorination
Check for:
– Error codes.
– Reduced flow.
– Leaks.

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For more details and specific procedures, check out this brochure from the provincial government.