Sounds like one's going to land in water (4)
I believe the answer is:
isle
'land in water' is the definition.
(an isle is a bit of land surrounded by water)
'sounds like one's going to' is the wordplay.
'sounds like' shows a homophone (sound like).
'one' becomes 'I' (Roman numeral).
'going to' becomes 'll' (as in he'll, we'll etc).
'i'+'ll'='ill'
'ill' is a homophone of 'ISLE'.
(Other definitions for isle that I've seen before include "Dogs, say" , "Man's one" , "Little land" , "Insular place" , "Geographic location" .)