What is shock chlorination?
Shocking a well or disinfection involves adding a strong chlorine (bleach) solution to the well and plumbing system to kill bacteria and other microorganisms in the well and the distribution system.
Who can shock/disinfect a well?
If any regulated activities (e.g., drilling, altering, developing or repairing the well or pump) are done, a registered well driller, registered well pump installer, or qualified professional to supervise the work are required to disinfect the well as part of regulated well work.
A registry of qualified well drillers and pump installers can be found at https://apps.nrs.gov.bc.ca/gwells/registries.
A private well owner can disinfect their own well but care must be exercised to do it safely and effectively. For wells that are hard to disinfect a qualified well driller or pump installer should be consulted.
When is shock chlorination/disinfection done?
After a well has been drilled, altered, developed or rehabilitated, or a pump has been installed, it is required that the registered driller or pump installer promptly disinfect the well.
It is a common maintenance and troubleshooting practice for private well owners when tested water has a positive bacterial result.
It is not always the best or permanent solution; it is not a long-term treatment strategy.
Is there anything I need to do before disinfecting the well and plumbing system?
Before disinfecting the well, an inspection should be done:
- 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.
What if I get another positive bacteria result after disinfecting?
Repeated positive bacteria results usually indicate a structural or environmental issue that requires professional evaluation or continuous water treatment.
Shock chlorination/disinfection only inactivates or eliminates microorganisms in the well, on the pumping equipment or in the distribution system. It will not eliminate bacteria in the aquifer beyond the immediate location of the well. If there is an external source of contamination the problem will only be solved temporarily.
Private well owners should test their water regularly and consult with a qualified well professional or local health folks before relying on repeated shock chlorination/disinfection.
Repeated shocking without fixing the cause is not recommended.
What are the advantages to shocking?
- It is effective at killing bacteria and many harmful microorganisms including coliform bacteria and E. coli that may enter a well after flooding, repairs or system disturbance.
- It is inexpensive compared to installing a treatment system.
- It is a quick way to disinfect the well and plumbing system.
- It is useful after maintenance or repairs for any time after a well is opened (pump replacement, well deepening, or plumbing repairs) to reduce the risk of introducing bacteria.
- In some cases it can temporarily improve water taste and smell from sulfur or nuisance odour causing bacteria.
What are the disadvantages of shocking?
- Shocking can be hard on plumbing and equipment as high chlorine concentrations can corrode metal components, damage rubber seals and shorten the lifespan of pumps and water heaters if done too often.
- Shocking only treats biological contamination. It doesn’t remove nitrates, metals, pesticides, PFAs or other chemical pollutants.
- Chlorine is hazardous in concentrated forms. Improper mixing or ventilation can cause health risks, including skin irritation and harmful fumes.
- The water is unusable during treatment. It can take a day or more to fully flush chlorine from the system.
For more details and specific procedures, check out this brochure from the provincial government.