CWWA lists recommendations on how to reopen buildings


Building owners/operators should flush out the water supply system when re-opening a building as bacteria can grow during a prolonged state of stagnancy. 

The Canadian Water and Wastewater Association (CWWA) has released guideline documents for building owners and operators looking to re-open buildings during the COVID-19 pandemic.

“When buildings are closed or on low occupancy for any prolonged period, water in the building becomes stagnant and can pose serious health risks. Harmful microbiological and chemical contaminants can grow or leach into water supply,” reports part one of the documents.

Part one is a “General Guidance for Water Utilities” and provides advice on steps to take to prepare for increased flushing, recommendations for distributing information to building owners, and guidance on communicating with the public and media. The CWWA also released a fact sheet for building owners and operators, which includes general instructions for flushing and cleaning water systems with a list of more detailed resources.

It is up to water utilities to get clean, safe drinking water to each property in relation to provincial and territorial regulations, said the CWWA. Prior to re-opening or fully re-occupying a building, building managers need to take steps to flush stagnant water, clean taps and fixtures and test that the water in their building is safe.

If a system is not actively maintained, the water becomes stagnant within the pipes, equipment, and storage tanks. “The disinfectant residual decays and disappears, hot water systems can become cooler and cold-water systems can become warm.” This can lead to microbial growth, lead and copper in the system, along with disinfection by-products.

Shutdown stage

During the shutdown, building owners and operators are advised to make a plan. This includes making a map or sketch of the entire system, including all equipment, pumps, tanks, and valves. They should identify all points of potential cross-contamination and all piping materials and know how they react.

Next, building operators should consider water pressure throughout the system and where it might have stagnation in areas of potential low pressure. Building operators should keep a detailed log of all maintenance conducted, tests conducted and all results. Moving forward, a full water management plan, including protocols and schedules, is recommended.

Routinely flushing the system becomes an important task – CWWA recommends weekly flushing but site-specific flushing guidelines should be developed as part of the long-term water management plan.

Hot water tanks should be kept above 60C to ensure hot water is kept above 50C throughout the system.

Re-opening building

When opening up the building to the public, another round of flushing is recommended by CWWA. This would be a more rigorous and extended flushing than regular maintenance, intended to not just replace the stagnant water, but also to dislodge sediment and biofilms.

Cleaning of fixtures such as taps, fountains, showers and connected food units, as well as any key components such as mixing valves and filters.

In addition, building operators and owners may need to consider disinfecting the system by circulating water with high concentrations of chlorine. But this need may only be considered for complex systems with storage or remote zones, buildings serving very vulnerable populations or buildings with a history of microbial issues.

To see the full checklist and list of recommendations, visit


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