Pools should be disinfected continuously by a chemical which imparts a residual effect. Chlorine is a type of “disinfectant”, also called a “sanitizer”. Disinfectants or sanitizers destroy living microorganisms and bacteria, preventing the transmission of disease. There are several types of disinfectants, such as chlorine, bromine, ozone and UV light. Public pools need a disinfectant with a measurable residual.