If you're in Rome or planning on a visit in the very near future, make sure you're prepared for the heat. Always have a plastic bottle with you so you can refill it at the numerous water fountains through out the city.
By all means dip your feet in the fountains like the one shown above at Piazza di Spagna (just remember to have respect. They are monuments and pieces of art and should not be abused).
Remember to apply sun cream to avoid burning.
Wear a hat and try to keep out of the sun in the hottest hours (10am-2pm).
Dress appropiately. The hot weather means people tend to dress minimal. While it's normal to see people in shorts etc remember that this is a holy city as as such you will be asked to cover up when entering certain areas. If you plan on visiting churches opt for knee length and cover shoulders. If you really can't stand the idea of not wearing a vest top make sure you have a shawl to cover up with when needed or you may find you get denied access to some places.