generally speeking, urine is sterile unless you have a bladder infection so i would try not to worry. and if there is infected urine in the pool it would be pretty well instantly disinfected by the chlorine or other sterilizing methods that are more than likely required by law.
you shouldn't be worried about it. i pee in the lakes around here but thats a much bigger volume of water than a pool and much less people. also theres fish in the lakes to so your swimming in fish and bird scat anyways. oceans just filthy period but i swim in that to.