Soda water contains Carbonic acid.
What is soda water?
Soda water is carbonated water. It holds water into which carbon dioxide gas under pressure that has been dissolved. The large majority of carbonated water is marketed in drink bottles as soft drinks and beverages.
Carbonated water is acidic
Carbon dioxide and water react chemically to yield carbonic acid, a weak acid that’s been presented to stimulate the same nerve receptors in your mouth as mustard. This triggers a burning, prickly sensation that can be both irritating and enjoyable. The pH of carbonated water is 3–4, which means it’s slightly acidic.