Water barrier (3)
I believe the answer is:
dam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">water barrier</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 dam that I've seen before include "eg Aswan" , "Animal's mother" , "Mother of quadruped" , "Barrier to hold back water" , "Water retainer" .)