About 1 in 5 people have admitted to peeing in a swimming pool at least once, according to a 2012 survey. And if you’re asking Olympic swimmers, well, that rate is much higher: nearly 100 percent, said Carly Geehr, a former member of the U.S. national swim team.

The American Chemical Society (ACS) estimates that there are somewhere between 30 milliliters and 80 mL (1 to 3 ounces) of pee per person in a pool. And one study from 1997 estimated an amount in the middle: an average of 70 mL (2.4 ounces) of pee per person.