About one in five Americans say they’ve peed in the pool. Even the world’s most famous pool-user, Michael Phelps, says “everybody” does it. Now scientists have finally figured out a way to quantify just how much urine is in our pools. A research team testing 31 pools and hot tubs in Canada found evidence of urine in every single one of them. On average, there were 8 gallons of urine in a 110,000-gallon pool and 18.5 gallons of urine in a 220,000-gallon pool. The results were even grosser for hot tubs. One hotel hot tub was found to have three times the urine level of the worst swimming pool. While urine itself isn’t harmful, it can react with chlorine to create “disinfectant byproducts,” which can be. Still, researchers say they aren’t trying to turn people off of swimming; they’d just like to remind everyone to please not pee in the pool.