How soon prior to occupancy should domestic water systems in new buildings be disinfected, according to ASHRAE Standard 188?

The requirement to disinfect domestic water systems in new buildings prior to occupancy is grounded in the need to ensure water safety and minimize the risk of Legionella contamination. According to ASHRAE Standard 188, it's recommended that these systems be disinfected at least three weeks before occupancy. This timeline allows for adequate physiological flushing of the system, ensuring that residual disinfectant levels can stabilize and protecting new tenants or users from potential waterborne pathogens before they start using the water supply.

The three-week period is strategically set to provide enough time for thorough disinfection processes, testing, and verification of water quality. If disinfection happens too close to occupancy, there may not be sufficient time to monitor potential re-growth of bacteria or to confirm that the disinfection effectively eliminated pathogens. This practice serves as a preventive measure, reinforcing the overall health and safety guidelines related to plumbing systems in newer installations.