The odds are great that any public swimming pool you visit will have a good amount of human waste floating around in it, making it akin to a huge toilet bowl. That doesn't even account for other bodily fluids emitted from the nose or mouth, sweat or human skin follicles that may find their way into the pool.
Americans love to go swimming, so we’re talking about a large number of people who are exposed. The Centers for Disease Control and Prevention estimate that there are approximately 10.4 million residential and 309,000 public swimming pools in the United States. Each year, people older than six account for roughly 301 million swimming visits, as calculated in 2009. The CDC say that 36 percent of children ages 7-17 years old and 15 percent of adults swim at least six times during the year.
The CDC also claim that close to 57 percent of spas violate local environmental health codes, with about one in nine (11 percent) so severely violating health standards that it should be closed immediately.
The term for illnesses caused by swimming is recreational water illnesses (RWI), which are the product of germs ingested by breathing in mists or aerosols, swallowing tainted water, or contacting contaminants found in hot tubs, water parks, swimming pools, play areas, interactive fountains, and even lakes, oceans and rivers. Illnesses can be caused by contact with fecal matter or can be the product of contact with chemicals found in the water or evaporated chemicals that are now breathable in indoor air.