Salt water spring perhaps half gone (3)
I believe the answer is:
sea
'salt water' is the definition.
(I've seen this before)
'spring perhaps half gone' is the wordplay.
'spring perhaps' becomes 'season' (spring is a kind of season).
'half gone' suggests halving the letters.
'season' halved is 'SEA'.
(Other definitions for sea that I've seen before include "7 [ship] s on this" , "Cod's home?" , "Expanse of salt water" , "Caspian, e.g." , "Lesser ocean" .)