I doubt that very much. Pecunia non olet, remember? Money doesn't stink, said Vespasian to Titus, when the latter complained about his father for raising tax on urine.
Urine was a valuable ingredient for making leather and as an ingredient for cleaning. Urine was collected wherever possible. Shopkeepers kept jars ready for passers-by and customers relieve themselves in, then to sell the contents to leather makers. That's why Vespasian taxed it.
Apart from that, have you seen how high viaducts are? It's a pretty steep climb for a prank. Roman justice was harsh. I have absolutely no idea what a pissing prankster would get, but 20 hrs community service had to be invented yet. The very least one could expect was a severe lashing. Probably a lot more.
Certainly by the population who would not be amused if someone pissed into their drinking water. Rome didn't have a formal police force. There were the vigiles, a corps of firefighters and night watchmen formed out of slaves and ex slaves (that should give you an idea how low this public service rated into society). Even a formal office for prosecution did not exist.
Justice was handled much more handled by individuals themselves. Being arrested by the vigiles would be the least of your worries. If the crowd caught you in the act, you could expect some real hard justice. More than enough to stop most modern pranksters.