Why is chlorine residual monitored in drinking water distribution systems?

Monitoring chlorine residual in drinking water distribution systems is critical primarily to prevent microbial contamination. Chlorine is widely used as a disinfectant to kill harmful bacteria and viruses that can threaten public health. By maintaining an appropriate level of chlorine residual throughout the distribution system, water utilities can ensure that any pathogens that may enter the water supply are effectively neutralized before the water reaches consumers.

In addition to its role in microbial disinfection, chlorine also helps to maintain a barrier against recontamination as water travels through pipes. This is essential for protecting water quality from sources of microbial threat during distribution. The other choices, while related to water quality, do not directly pertain to the primary purpose of chlorine residual monitoring in terms of safeguarding against microbial hazards.