What does residual chlorine refer to in water treatment?

Residual chlorine refers to the amount of chlorine that remains in the water after the disinfection process has been completed. This aspect is crucial in water treatment as it is a measure of the effectiveness of the chlorination process and provides an ongoing level of disinfection as the water moves through the distribution system.

Maintaining a certain level of residual chlorine is essential for ensuring that any potential pathogens present in the water are continuously inactivated before the water reaches consumers. This residual also acts as a safeguard against recontamination that may occur after the treatment process, thereby contributing to the overall safety and quality of drinking water.

In contrast, other options do not directly relate to the function of chlorine in ensuring water safety post-treatment or in maintaining a disinfectant presence within the water distribution system.