"I think everybody pees in the pool," Olympic swimmer Michael Phelps told The Wall Street Journal last year. "It's kind of just a normal thing to do."
A recent study supports Phelps' assertion. Researchers in Canada tested 31 pools and hot tubs for urine. They found pee in every single one of them — 8 gallons' worth in a typical-size pool.
TODAY national investigative correspondent Jeff Rossen went undercover to collect samples from hotel swimming pools, hot tubs — even a water park — and send them off to a certified lab. Only one came back pee-free.
"Chlorine doesn't kill urine," NBC medical correspondent Dr. John Torres told Rossen. "That chlorine smell you get in the pool, it's actually urine mixed with the chlorine you're getting the smell from."
Aside from being gross, "there are some health risks because when that urine mixes with the chlorine, it makes two chemicals, cyanogen chloride and trichloramine. Those chemicals can irritate your eyes, they can irritate your lungs, they can irritate your skin," Torres explained.
He added: "The main thing is, don't pee in the pool! Tell your family and friends: Don't pee in the pool."
Unfortunately, according to a recent study, 64 percent of Americans say they pee in pools. And experts say there's only one way to get rid of it: Empty all the water out and refill the pool.