Sound of water we hear (5)
I believe the answer is:
creak
'sound' is the definition.
(creak is a kind of sound)
'water we hear' is the wordplay.
'water' becomes 'creek' (creek is a kind of water).
'we hear' indicates a 'sounds like' (homophone) clue.
'creek' sounds like 'CREAK'.
'of' acts as a link.
(Other definitions for creak that I've seen before include "Audibly reveal weakness under strain" , "Screech, grate" , "Squeaking sound" , "Groan (like a loose floorboard)" , "harsh squeal" .)