Last I looked into it only about 1/3 people pee in the pool (excluding toddlers and young kids), but that's enough people that pretty much every public pool is gonna have pee in it.
Yep, every public pool, every outdoor pool, and every pool that ever has small kids in it has pee in it. Which is basically every pool. Also it's that a third of adults have admitted to peeing in the pool, so that number is likely much larger. That super strong "chlorine" smell that people associate with pools isn't chlorine, it's chloramine, which is, as my boss put it, "Chlorine bonded to "stuff"". "Stuff" being literally anything that isn't water. This includes pee, but also lotion, make-up, hair gel, everything. If you get bright red eyes from the water you don't wanna be swimming in it. A little red is expected, everyone having bloodshot eyes? Nope nope nope, you will not catch me in that water.
As a former lifeguard, I can confirm that number is a ridiculous underestimate. People would be staying for hours and hours, drinking gallons of beer or whatever and maybe one person would enter the bathroom per 10 people. Honestly 2-7 year olds were the best about it, but nearly everyone else admits to peeing in pools or is a dirty liar.