So to flush this myth once and for all ACS Reactions visited San Francisco's Aquarium of the Bay to discuss the real science behind the process:
..the amount of acid you’re looking for just isn’t in urine. While your pee IS acidic, usually with a pH of around 6, it isn’t acidic enough to denature porins and prevent them from hole-punching your cells. And the same goes for rinsing with fresh water. …Your best bet is to find a safe, jelly-free area in the same body of water where you were stung and rinse the affected area with salt water.