Rome doesn’t have a lot of public bathrooms and there’s an urban myth circulating for years which says that Rome has a law that all bars and restaurants need to allow non-customers the use of their bathrooms. That’s false!
The true law states that: all bars and restaurants need to have a working bathroom for their customers.
The myth comes from another law which states that bar owners can’t (a) charge you for the use of bathroom and (b) claim that the bathroom is out of order. In the latter case a potential customer, a person who hasn’t bought anything yet, can call the police and they can close the bar for a day and fine the owner.
In all that in mind, what do you do?
Well, from my experience no one would mind if you simply walk in casually and use the bathroom in a crowded bar. I also believe, although it contradicts my one and only experience, that the owner of an empty bar would let you use the bathroom if you ask nicely instead of storming the place, walking like you own it and asking the owner where’s the toilet.
If you’re not in a hurry, use the time and buy an espresso for €1 and enjoy it without worrying whether a staff member will come to bug you about using the bathroom.
I wouldn’t be able to share this information without a help from a fellow Redditor RomeVacationTips. If you’re traveling or planning to travel to Rome I recommend checking out his awesome website where you can learn so many useful things like how to skip the 30 minutes line to the Colosseum, how to see the Pope for free and why you should never by water in Rome.