But surely it doesn't contain rose water! (6)
I believe the answer is:
redsea
'but surely it doesn't contain' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'rose water' is the wordplay.
'rose' becomes 'red' (shade of red).
'water' becomes 'sea' (the sea is water).
'red'+'sea'='REDSEA'
Can you help me to learn more?
(Other definitions for redsea that I've seen before include "mass of water" , "Waterway" .)