A water bed? (7)
I believe the answer is:
channel
I believe this clue is a double definition.
'a water' is the first definition.
(I know that channel is a type of water)
'bed?' is the second definition.
(I've seen this before)
(Other definitions for channel that I've seen before include "Communication medium" , "Narrow body of water between two land masses" , "Passage for fluid or communication" , "Bed of a stream; medium" , "Water conduit or TV programme identifier" .)