Swimming pool contamination can originate from environmental sources and swimmers. Outdoor pools are particularly vulnerable to environmental contaminants, including windblown dirt, debris, unsanitary incoming water, rain carrying microscopic algae spores, and bird droppings that may harbor disease-causing pathogens. While indoor pools are less affected by environmental contaminants, they can still be impacted by contaminants introduced by swimmers.

Swimmer-induced contaminants can significantly affect the operation of both indoor and outdoor pools. These contaminants include microorganisms from infected swimmers, body oils, sweat, cosmetics, suntan lotion, urine, saliva, and fecal matter. Studies show that, on average, swimming pools contain 30 to 80 ml of urine per person who uses the pool.