In Ukraine and really all of Europe, carbonated water/sparkling water/water with gas is given as an option besides water "without gas". If you want regular water you must specify it or you will get carbonated water. So, this sentence would be used to talk to a waiter, or a shopkeeper, asking if they have sparkling water or water with gas to drink.
I second the thought that both "gas water" and "water with gas" are horrible translations, although I've heard it said hundreds of times by Americans living in Ukraine (in Germany they call it 'bubble water'). The best translation is "Do you have carbonated water", but I decided to give "Do you have water with carbonation" a try, which also failed. The question is just a nightmare for this type of program.