Water in the hose attachment (3)
I believe the answer is:
sea
'water' is the definition.
(the sea is water)
'in the hose attachment' is the wordplay.
'in' says the answer is hidden in the clue.
'SEA' is hidden in the letters of 'hose attachment'.
(Other definitions for sea that I've seen before include "Eg, Aral, Ross, Irish" , "North, say" , "that's easily reached from Dover?" , "North for one" , "Watery expanse" .)