food is also a basic neccesity, but if you go to a restaurant...
I'd argue even the cheapest food will cost more than a carafe of tap water, which only takes seconds to fill.
It's like getting free peanuts with your beer. The bar is probably paying a few cents out of its pocket but they make you more thirsty so...
Besides in France tap water is part of the cover charge in restaurants. You're legally entitled to it. Unlike a glass of water in cafés but yet it is customary in most places you'll get a free one with your coffee if you ask for it.
In Paris, Venice, Rome, the Riviera, etc you are gonna get nickled and dimed over stuff. You order water and get a 3 euro bottle of San Pelligrino and the table of locals next to you gets a free carafe of still water. That's just how it goes when you're a tourist.
As I said, in France it's legally part of the cover charge so you can raise a fuss. Be sure to ask explicitly for tap water. There should be no doubt when asking for a "water carafe" but I could see some owners playing dumb with tourists.
That said, San Pellegrino is the superior choice to accompany a meal so there's that !