What does the term "residual" refer to in swimming pool maintenance?

The term "residual" in swimming pool maintenance refers to the concentration of a chemical in the water. This concept is crucial for ensuring that the pool water remains safe and clean for swimmers. For example, in the context of chlorine, the residual level indicates how much active chlorine remains in the water after chemical addition and after it has been used to sanitize the pool. Maintaining an appropriate residual concentration helps to effectively kill bacteria and other pathogens while also preventing algae growth.

This term is integral to water quality management because if the residual levels are too low, it can lead to inadequate disinfection, which poses health risks to swimmers. Conversely, too high a concentration can lead to irritation and discomfort for users. Therefore, regular testing and monitoring of chemical residues is a fundamental aspect of pool management and maintenance.