What does chlorine residual refer to in water treatment?

Chlorine residual refers to the amount of chlorine that remains in the water after disinfection has occurred. It is important for maintaining a safe drinking water supply, as the residual chlorine continues to provide protection against bacterial growth as water moves through the distribution system.

In the context of water treatment, when chlorine is added to water, it reacts with contaminants and pathogens, effectively killing them. The portion of chlorine that does not react and remains in the water is known as the residual. This residual is crucial because it indicates the effectiveness of the disinfection process and helps ensure that the water remains safe as it reaches consumers.

The other options focus on different aspects of chlorination: the total amount of chlorine used describes only the input rather than the effective leftover; the process of adding chlorine outlines the activity rather than its result; and the amount of chlorine consumed refers solely to what has reacted and does not account for what is left behind. Thus, the defining aspect of chlorine residual is specifically concerning the amount available after the disinfection process, making it a key parameter in water treatment management.