Carbonated water is available in pretty much all groceries here in the US Midwest, but usually as a specialty drink. San Pellegrino and Perrier as “exotic” European bottled waters (despite cheap prices), Topo Chico and other aguas con gas in the Hispanic/Mexican aisles and tiendas. Maybe $1 for 500 ml, less than $2 for a full liter, but it’s still considered unusual. (It was an eye-opener to take Spanish language/culture classes and discover that carbonated waters were the norm elsewhere.)
That said, I find it hard to guzzle a liter of San Pellegrino in less than a day, but can down a 2 liter of soda in minutes. I think it’s the root of carbonated water’s niche popularity in the US- in general, we prefer drinks we can guzzle with abandon (juice, agua sin gas, sweet sodas), while carbonated waters seem to only be sippable.
We have that, but also cheapass seltzer in 2L soda bottles. Which I suppose is as expensive as soda so there’s not much point in adding packets to seltzer except as an experiment.
However, soda flavoring is specifically formulated to offset the taste of carbonation, which is part of the reason is doesn’t taste as good flat. It should be simple to reformulate it for non carbonated water. I’ve had coke flavored ices and they taste great.
In many smaller grocers or convenience stores, they’re not to be found at all, and even in the big ones, carbonated waters are usually found in the alcohol mixers section – at least in my part of the country. There are the imported brands, but also the garden variety Faygo and Canada Dry. These are usually sold as “club soda” whereas the imported stuff is sold as “mineral water” or “sparkling water.” In certain parts of the country, I imagine the commercial stuff would be sold as “seltzer.” Strictly speaking, there are some differences, in that club soda has some additional mineral content added, etc. In restaurants that don’t sell mineral water, you can usually just ask for plain old “soda water” which the bar wand dispenses (soda without syrup).
Interestingly I recently came across a Canada Dry Club Soda fountian dispenser. I’m guessing that the Club Soda dispenser simply didn’t have a syrup line connected to it, whereas the rest of the soft drinks worked normally. But… club soda has added (non-sodium) salts.
In any case, I have no problem putting away 2L of homemade sparkling water in a single day. Since I don’t really drink soda-pop, it’s either beer or bubbly water, and the bubbly water is a lot more healthful and has a lot fewer calories!