Fizzy water (4)
I believe the answer is:
soda
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fizzy water</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for soda that I've seen before include "kind of water" , "for use with whisky?" , "Soft drink" , "Sodium carbonate" , "Mixer drink" .)