What is the recommended minimum retention time for water to sit in a newly disinfected main?

The recommended minimum retention time for water to sit in a newly disinfected main is 24 hours. This retention period is essential to ensure that the disinfectant, typically chlorine, has adequate contact time with the inner surfaces of the water main. This contact time is critical for effectively killing or inactivating harmful microorganisms that may be present in the system after construction, maintenance, or repair activities.

During the 24-hour retention period, the disinfection process allows for sufficient penetration and reaction of the disinfectant with pathogens and biofilms that may be inside the pipes. This helps to ensure the safety of the drinking water supply and the health of individuals consuming the water. Moreover, after the retention time, it is advisable to conduct water quality tests to confirm that the disinfectant residual levels are appropriate before the water is released into the distribution system.