When using the combined available chlorine residual (CACR) method, how should the CACR be adjusted when water temperature decreases?

The correct approach when using the combined available chlorine residual (CACR) method in response to a decrease in water temperature is to increase the CACR to maintain proper chlorine residuals. This is because colder water typically reduces the effectiveness of chlorine as a disinfecting agent. As water temperature falls, the reaction rate of chlorine decreases, which can lead to inadequate disinfection if the residual concentration remains unchanged.

To ensure effective disinfection and prevent the growth of pathogens, operators must compensate for this reduction in activity by increasing the CACR. This practice helps ensure that adequate chlorine levels are maintained in the water supply, promoting public health and safety.

While it might seem reasonable to consider that low temperatures could allow for lower chlorine levels, the science behind chlorine disinfection indicates that achieving effective microbial inactivation requires adjustments to residual levels when conditions change. Therefore, determining the right adjustment is crucial to maintaining adequate disinfection standards.