You have been swimming in pee
It's no surprise that public swimming pools might have some pee in it. But the amount of it has always been difficult to measure, or estimate. But now Xing-Fang Li from the University of Alberta say that they have been able to roughly estimate the amount based on the measurement of the artificial sweeteners carried in most people's urine.
According to their calculations, a big 220,000-gallon commercial-size swimming pool contains around 20 gallons (75 litres) of pee.
"I think you can assume that if people are using your pool, they're peeing in it," -- Ernest Blatchley III, an environmental engineer at Purdue University.
So what can you do about it? Well, like they say, if you can't beat them, join them!
Or better yet, just don't swim in pools.