Desire for water (6)
I believe the answer is:
thirst
'desire for water' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for thirst that I've seen before include "The inducement for 5 Down" , "Strong desire for drink" , "Want of drink" , "A craving for drink or knowledge" , "Craving for liquid" .)