Here's something to think about the next time you dive into a pool.

Researchers tested 31 pools and hot tubs in Canada and found evidence of urine in all 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, USA Today reported.

But the results were even worse for hot tubs. One hotel hot tub had three times the urine level of the worst swimming pool, according to the study in the journal Environmental Science & Technology Letters.

Urine itself isn't a threat, but can react with chlorine to create "disinfectant byproducts," which can be harmful, USA Today reported.