Common liquid (5)
I believe the answer is:
water
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">common liquid</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 water that I've seen before include "Superior's full of it" , "Commonest fluid" , "Give fluid to (plants)" , "H2O" , "It's to be found in puddles, pools and ponds" .)