Hmm. Probably the only moment you can pee during a race is during a breaststroke withdraw. You spend so much time gliding that if you really needed to go, you could probably go. The other options are backstroke or butterfly. In backstroke, you would need to surface to void your bladder, but in the beginning of the race it might not be possible to do so safely. And in butterfly, you would need to have some sort of floatation device like a noodle to help you swim faster. So basically you can't pee during a race. When they return from the pool, they wet themselves down with water and dry off using towels provided by the coaches. However, there is some evidence that swimmers may retain some urine while swimming. A study conducted at the University of North Carolina at Chapel Hill found that young swimmers retained up to half of their fluid intake. This is likely due to the intense exercise required by swimming causing the body to produce more antidiuretic hormone (ADH), which causes the kidneys to release more urine than normal to keep the salt concentration in the blood stream constant. As long as this situation is maintained, the swimmer will not die from dehydration even though they are sweating heavily!