One thing Rome is not short of is fountains. There are around 300 monumental fountains as well as many small public drinking fountains. Estimates vary wildly, but altogether there are something like 2000 fountains in the city.
Most famous of all, is the Trevi Fountain. Every tourist will at some point head there. Many of them will throw the traditional coin into the water to ensure that they return to Rome.
Equally, I like the three fountains in Piazza Navona. Two of them (Fountain of the Four Rivers and the Fountain of the Moors) were designed by Bernini, the Baroque genius. So popular was he at the time, that 9 different popes commissioned works by him.
The largest, the Fountain of the Four Rivers is a marble extravaganza. The four river gods are dramatic, twisting figures, with outstretched limbs, straining muscles and swirling robes. Horses appear to leap from the stone and the whole thing is unexpectedly topped off with a towering Egyptian obelisk.
Incredibly, Rome’s fountains do not rely on mechanical pump systems. Instead, they rely entirely on gravity which is only possible because the water supply comes from an elevated source, higher up in the surrounding hills.
Interestingly, this was a critical factor in design. The higher the water source, the higher a fountain’s water jet could shoot into the air. So some fountains, like the one in St. Peter's Square could reach up to 20 feet. In contrast, the water pressure was nowhere near as high in Piazza Navona so these fountains were designed so that the water cascaded, rather than shooting upwards.