Some land in water, carried towards the surface? (4)
I believe the answer is:
acre
'some land' is the definition.
(unit of land)
'in water carried towards the surface?' is the wordplay.
'in' indicates the answer is hidden within the clue.
'towards the surface?' says the letters should be written backwards (in a down clue, letters go up).
'erca' is hidden within 'water carried'.
'erca' in reverse letter order is 'ACRE'.
(Other definitions for acre that I've seen before include "Israeli seaport" , "amount of land" , "Imperial land measurement" , "4840 sq yds" , "stretch of land" .)