The Wall Street Journal headline asserts, “The Dirty Secret of Olympic Swimming: Everyone Pees in the Pool”. Two main reasons. The swimmers are super-hydrated and their speed suits take 20 minutes to take off and put on. Chlorine for the win.
There’s an unspoken rule that you don’t let loose near others. That is, most swimmers most of the time. Apparently, there are some exceptions.
For the record, I would never whizz in any body of water that’s not encased in porcelain.
Pressing Pause 
But if you’re working outside (battling flames, cutting lawns (my dear old father’s job)), and you’ve got to go, a paper cup will suffice.