The Porter, Not His Only Job
All of the fans of roman fountains may have come to the purpose of this story. The porter, who at night gathered water from the Trevi, so he could sell it the following day, was not just a porter. He was a water seller, or an acquarolo. To take water from the Trevi you have to pay dues. The law was that an aquarolo who took water from the Trevi, year round, “must pay five Julii in all: idem, for all horses and mules that take on water from the fountain five balocchi must be paid for each beast". So who were the watersellers? There were, in total, 965 baths and 1352 public fountains, all of these were fed from 19 aqueducts. This lasted until 537 when Vitige, unable to defeat the Romans, decided to obstruct the aqueducts. At the same time, Belisario, trying to prevent the enemy from getting inside the city blocked the mouths of the aqueducts. So with the aqueducts being blocked the Romans have to rely on the Tiber, which they had to go to the river, and get enough water to store for days at a time. Therefore the acquaroli came out of the fact that the Romans found it bothersome to constantly need to go for water, and it was much easier for it to be brought to them.