If you've ever peed in a pool, you know that the whole "the water will turn colors and we'll know you did it" thing is a total urban myth. But the lack of poolside justice doesn't mean you shouldn't feel guilty about what you did. The latest news—a study of 31 public swimming pools and hot tubs in Canada—shows that mid-swim peeing is a pretty big problem.
A team of researchers from the University of Alberta, Edmonton, found that 100 percent of the pools and tubs they sampled tested positively for acesulfame potassium (ACE), an artificial sweetener commonly found in processed food that passes through the body unaltered. (Translation: pee.) One Olympic-sized pool (830,000 liters total) had about 75 liters of urine in it, according to the study. To help you visualize: that's like dumping 75 full Nalgene bottles of pee into a competitive swimming pool. UM, gross.
We kinda already knew how many people were guilting of going number one in the water; about 19 percent of people admitted to having peed in a pool in a 2012 study by the International Journal of Aquatic Research and Education. But knowing how much of it is swimming around with us is an unsettling reminder that going for a dip or logging some laps in the pool isn't a purely healthy, recreational activity as we might think. (Here's what Olympic swimmer Natalie Coughlin thinks about peeing in the pool.)
But that's what chlorine is for, right? Not so fast, Phelps. Pools are loaded up with disinfectants to protect still water from breeding scary bacteria (like salmonella, giardia, and E. coli), and those disinfectants undergo chemical reactions with the organic matter (read: dirt, sweat, lotion, and—yep—pee) that humans introduce into the pool, according to this video by the American Chemical Society. These reactions create a thing called disinfection byproducts (DBPs). Urine specifically contains a lot of urea, which combines with chlorine to create a DBP called trichloramine, which causes that classic pool smell, as well as red, irritated eyes, and has been linked (like most other DBPs) to respiratory issues like asthma. And although other organic matter does contribute to the DBPs in pools, urine is responsible for half the DBPs produced by swimmers. Somes pools were found to be 2.4 times more mutagenic (filled with gene-altering agents) and hot tubs were 4.1 times more mutagenic than basic tap water, according to another study in the journal Environmental Science & Technology. (More on that: How Gross Your Gym Pool Really Is.) A large portion of those came straight from urea, according to the researchers. (And this doesn't even count the other scary parasites swimming around in public pools, ponds, lakes, and water parks.)
We'd never tell you to skip your next swim, but we will tell you to empty out your bladder beforehand. And make sure to hit the showers pre-swim—that'll mean less dirt and sweat going into the water.