Drainage area (5)
I believe the answer is:
basin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">drainage area</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for basin that I've seen before include "Round open dish for water" , "River-drained area" , "Water receptacle" , "Washbowl" , "Dock - vessel" .)