Under what condition would chlorine residuals in water storage facilities be likely to decline?

The decline of chlorine residuals in water storage facilities is most likely to occur during low use periods. When water demand is low, there is less turnover of water in the storage system. Consequently, water can remain stagnant for longer periods, allowing chlorine to dissipate more rapidly due to various factors such as temperature, water quality, and the presence of organic materials that react with chlorine.

In contrast, heavy rainfall events typically increase the flow of water into the distribution system and may introduce additional water that could be treated with chlorine, possibly maintaining or increasing residual levels. Changing the water source can alter the characteristics of the chlorine residuals based on the new water’s chemical makeup, which may lead to a decline but is not as consistent as low usage periods. During peak usage hours, water is moving through the system more quickly, and the continual turnover helps maintain chlorine levels rather than allowing them to decline.