Never ask for tap water in an Italian restaurant. It will end up costing you €3000.
https://www.bbc.com/news/articles/c4g4yd8q0j7o

Common sense in the courts!

Yes. The case must have cost a fortune. Legal fees in Italy are eye watering.

But really why would you? In most decent family run trattorie bottled water is cheap enough.
My tip is to try and find a brand that is named after a Saint as you know that the water would have been passed by monks and nuns

Credit to the waiter for not giving away the old trick of sticking tap water in a fancy bottle!

Its is quite normal to see men loading up water from roadside drinking fountains. They are sometimes mechanised where you pay 5 cents for a litre.(still or sparkling) I suspect restaurants are using these places where 5cents can be easily converted into €5.