One looks for water (6)
I believe the answer is:
dowser
'one looks for water' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for dowser that I've seen before include "He uses a divining-rod" , "Water-diviner" , "Detector of underground water" , "One uses a divining rod" , "One who locates water with hazel stick" .)