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Re-Open Your Business: The Safety of Your Water

​COVID-19 response has forced prolonged closure or reduced occupancy of many buildings. As restrictions begin to be lifted, building operators and owners need to be aware of issues that can threaten the safety of water and sewer services in their building (CWWA, 2020).

The City of Lethbridge Water Utility would like to remind building operators that the water inside their building's plumbing may have been sitting there for the last several weeks and could have become stagnant and can pose serious health risks.

Stagnant water can lead to:

  • Low chlorine levels
  • Colour, taste, and/or odour issues
  • Increased lead, copper, and Legionella levels at the tap

The effects of stagnation will vary between each building, based on:

It is the City's responsibility to provide clean, safe drinking water to each property. It is the responsibility of each property owner to maintain the safety of that water within their building.
  • length of shut down
  • size of the building
  • number of occupants
  • complexity of the system
  • state of the piping
  • maintenance performed during shut down

Information obtained from the Canadian Water and Wastewater Association (CWWA).

Flush the plumbing

If your building has been empty for more than two or three weeks, you will need to flush the plumbing in your building, providing the plumbing with fresh water from the water distribution system.

CWWA suggests the following maintenance and mitigation during a shutdown. All details are listed in the                Safely Re-Opening Buildings - A Fact Sheet for Building Owners/Operators.




How do I flush my water system?

 The Checklist provided by CWWA, includes the following for flushing your system:


  • treatment equipment, pumps, valves, tanks, etc
  • all outlets, fixtures such as taps, fountains', showers, etc
  • include all connected food unit, such as ice or coffee makers


  • Start where the water enters the building and work from closest to furthest, closest zone to furthest zone, closest outlet to furthest outlet. Flush your cold water system first then your hot water system.

Note: Hot water tanks should be kept above 60˚C to ensure a temperature over 50˚C throughout the system.  Be sure to flush the tank fully to replace all of its water.  You may consider draining the tank, but be cautious as this could stir up sedimentation or cause syphoning concerns. Then flush the hot water system from closest to furthest from the tank.

  • Flushing requirements vary but run the water until the water maintains a constant cold temperature and the disinfectant (like chlorine) is detected.
  • This should be a rigorous flush so you want to open taps fully (remove the aerator filter or shower head) but be aware this could cause greater spray and aerosols.
  • Staff should wear appropriate PPE such as gloves, mask (N95 is recommended), and eye cover while flushing.


  • If possible, clean, disinfect and rinse all outlets, screens etc.


  • Shock chlorination may only need to be considered if you have a large system with remote branches, storage tanks, or you still detect issues after flushing, if you serve vulnerable populations or have a history of pathogen problems
  • Such system shocking should be conducted by a water treatment professional


  • For smaller buildings, after flushing, you should be able to feel a consistent cold temperature and even detect disinfectant (such as chlorine by smell).
  • For larger buildings and any building serving vulnerable populations, professional testing is highly recommended.
  • Testing for disinfectant residual - simple equipment and/or testing services are available from local water treatment companies, plumbers and pool professionals.
  • Testing for microbial pathogens – for complex systems, buildings serving vulnerable populations, or any with a history of contaminations (like Legionella) – these issues are often related to water in HVAC systems.  Your local health unit should be contacted for assistance.

Other Resources to help you flush your system:

The Building Water Quality and Coronavirus: Flushing Guidance for Periods of Low or No Use from the Environmental Science Policy & Research Institute further outlines how to flush based on the size or type of building.



Resources and Articles:

Alberta's Relaunch Strategy

Re-Opening Guidance Documents

Center for Disease Control and Prevention (CDC)



For more information

Online: Submit a service request
Phone: 311 or 403-320-3111 (if outside of Lethbridge)
Address:  City Hall, 910 4 Avenue South, Lethbridge, Alberta, T1J 0P6