In segments of the domestic cold water system (DCWS) that are stagnant for two days, what is expected regarding free chlorine levels compared to segments used frequently?

In segments of the domestic cold water system that experience stagnation for two days, it is expected that free chlorine levels will be lower compared to segments that are used frequently. This occurs due to several factors related to water quality and the behavior of chlorine in stagnant water.

When water sits still for an extended period, such as two days, the disinfectant properties of free chlorine diminish due to various chemical and biological processes. Chlorine can react with organic matter and biofilm that may develop on the surfaces within the pipes, leading to a reduction in its concentration. Additionally, the absence of flow prevents the continuous replenishment of chlorine that would typically occur in regularly used segments of the system.

As water is drawn from regularly used sections, fresh chlorine is introduced, helping to maintain higher levels of free chlorine. Conversely, stagnant water allows for potential growth of microorganisms, which can further deplete chlorine levels as the disinfectant is consumed.

Thus, the expectation of lower free chlorine levels in stagnant segments is consistent with water quality management principles aimed at preventing microbial growth and maintaining effective disinfection in plumbing systems.