(Whilst it is not possible to find the actual culprit (the colour of the water doesn't change), after monitoring two public pools in Canada the researchers found that a typical large swimming pool ( a large pool (about one-third the size of an Olympic pool) contains 75 litres of urine – enough to fill a medium-sized dustbin.
If you don't swim in public pools, but you enjoy a spa experience, they also tested hot tubs, which were found to have far higher urine levels.
In one anonymous survey, 19% of adults admitted to having urinated in a swimming pool at least once. And it seems professional swimmers are the worst offenders, as they don't have "time" to get out and use the facilities.
Please! Eew! I can swear, with my hand on my heart that I have never peed in the pool. I always go before I swim (I honestly believed the water would change colour), and I shower and wear shower shoes too. It's not that difficult to do.)
This is why you shouldn't pee in the pool:-