Perish in water (5)
I believe the answer is:
drown
'perish in water' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for drown that I've seen before include "Suffocate in liquid" , "Die in sea" , "Kill by submersion" , "Immerse (fatally?)" , "Submerge, maybe fatally" .)