I've been in Italy for a month now and have natural sparkling water with most meals (sometimes drop in a little white wine in the same glass at lunch).
It can also help provide a sense of satiation if you are restricting calories at all.
There are a few dental studies that show it can have a slight to negligible effect on teeth enamel but no where near the effects of soda or fruit juices.
Shoot for ones with a good amount of dissolved mineral content.
I was wondering the same thing myself!! We bought a soda stream simply for the carbonation. We never add any kind of sweetener, we just love the fizz!!
It's just a dissolved gas; you'll burp much of it back out. Try making fizzy honey water sometime.
Why would you put sugar into water? Try a high silica low bicarbonate mineral water like Levissima which tastes very light
I love sparkling water but ones that are not too fizzy. My favourite is Pellegrino which I have with ice and a quarter of a lime or lemon squeezed into with the fruit left in the water. Very refreshing.