Most organisms that enter pool water are killed very quickly by the chlorinated water treatment. Some organisms have become resistant to disinfection, such as Cryptosporidia, E-Coli, and Giardia. Symptoms of these may not appear sometimes for more than a week after being infected. High-risk groups include diaper-age children and immuno-compromised persons (cancer patients, person with transplants, and persons with active HIV infections).

If a solid stool is in the pool, that section will be closed, the stool removed, and extra chlorine will be mixed into the water in that section The section will remain closed for about an hour, until testing shows that chlorine levels are appropriate for swimming.

If there is vomit or diarrhea in the pool, the entire pool must be closed, solid pieces will be removed, and the full pool will be super-chlorinated. The pool will remain closed for at least eight hours, until chlorine can be returned to appropriate levels for swimming and testing of every section indicates chlorine levels are appropriate.