"sparkling water" is "αεριούχο νερό". You can also say "ανθρακούχο νερό", άνθρακας means carbon (C).
"Μεταλικό νερό" is the natural water coming out of a spring, but it is not necessarily "sparkling water".
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.