What does the term "chlorine residual" refer to in water treatment?

The term "chlorine residual" refers to the small amount of chlorine that remains in the water after the initial application and the needed reactions have taken place. This residual is critical in ensuring ongoing disinfection as the water travels through the distribution system, providing protection against microbial contamination that may occur after treatment. It is important for water treatment systems to maintain an adequate chlorine residual to ensure that water remains safe for consumers.

In this context, the other options do not accurately capture the specific meaning of chlorine residual. While the first option mentions chlorine after filtration, it does not focus on the residual aspect integral to maintaining safety. The choice indicating total chlorine added overlooks the concept of consumption during reactions or potential losses over time. Finally, referring to chlorine levels before any treatment does not relate to residual levels after chlorination, which is essential for ongoing disinfection.