Scientists Can Measure Exactly How Much Pee Is in the Pool

Chances are, if you’re swimming in a pool, you’re touching at least a little pee. (Some of it might even come from the lifeguard.) But now scientists can figure out exactly how much is floating around, as NPR reports. A team of toxicologists at the University of Alberta discovered that by tracing the levels of artificial sweetener in the water, you can figure out roughly how much of the liquid is urine.

The sweetener acesulfame potassium doesn’t get processed by the body and doesn’t break down in the water, so it can serve as a proxy for the pee. In the study, researchers tested 250 samples from 31 pools and hot tubs in two Canadian cities, and found acesulfame-K in every one, indicating that pool pee is just as prevalent as you feared.

Some samples showed up to 570-times the amount of the compound you’d find in tap water. By monitoring levels in two pools over the course of three weeks, the researchers estimated that there were around eight gallons of pee in the 110,000-gallon pool and about 20 gallons in the 220,000-gallon pool. It’s not that much pee, in relative terms, but still, no one wants to imagine pouring 20 gallons of pee into a communal swim spot. (For reference, the average person pees up to half a gallon per day.)

Unfortunately, pee in the pool is more than just a little icky. The chemical cocktail of chlorine and pee is what makes your eyes red after a long day of swimming, and regular exposure can lead to respiratory issues. On the bright side, it would take a lot—really, a lot—of pee to kill you.