reporter: she may not. others do. according to a study from the water quality and health council, 1 in 5 people admit to peeing in the pool. i think more people than one out of five have done it but they just haven t admitted it. reporter: the people who clean pools also know what happens. that s why at this ymca pool in the bronx, new york they say they check the water every two hours. it s tough. you have to be constantly monitoring it. you have to be persistent in checking your levels. reporter: but a new report from the centers for disease control suggests this ymca and its high standards are more the exception than the rule. we found that almost 1 in 8 pools was immediately closed on inspection because of serious violations that threatened public health and safety. by serious violations i mean, for example, no chlorine in the water. reporter: that could leave swimmers unprotected from bacteria that could cause everything from an upset stomach to an e. coli infection.