From water, retrieve reversible piece of harness (6)
I believe the answer is:
terret
'piece of harness' is the definition.
(part of a horse's harness)
'from water retrieve reversible' is the wordplay.
'from' indicates the answer is hidden within the clue.
'TERRET' is hidden within 'water retrieve reversible'.
(Other definitions for terret that I've seen before include "Ring for reins on a harness (palindrome)" , "Swivel ring" .)