I get really irked in restaurants if I ask for San Pellegrino and they just give something else, or specifically claim that something else is the same. I am really annoyed when they bring Lurisia and say it's the same "Italian sparkling water".
San Pellegrino is full of minerals and stuff and has a distinctive taste. It is clearly MINERAL water in the real sense. Lurisia makes a point of being pure spring water, salt free, making a feature of being featureless.
Do restauranteurs really not know the difference, or do they sell what the get the best margin on, or do they just serve whatever they personally prefer?
I think the whole idea of a tasting menu of 20 different waters is kind of absurd and pretentious, but that doesn't mean that they are all the same, and in a restaurant where they claim that their particularl tomatoes or beef or chicken are specially better than others, why pretend all bottled water is the same?