RST has identified two fountains that are especially busy, crowded with tourists, locals, and the faithful slaking a thirst. Each, predictably, is located in the heart of a tourist area, and each has a certain style--even if that style is sometimes mediated by a plastic bottle or the crush of the needy.
The first, below, can be found in Piazza San Marco, that little rectangle of semi-sanity adjacent to Piazza Venezia and across the street from the Altare della Patria.
The second is just to the north of Piazza San Pietro [the right side, as one faces the basilica] - note the fountain's shape - Pope's hats and St. Peter's keys to the church.
Drink up, Rome.