I'd say 80-90% of the times, along with a "If you need anything else, please just let us know".

That said, they do try to be subtle when sliding the bottle across - had this one time when the lady sitting next to me (a first time CXflier) - asked for some water as well, just before take off.
They got her a glass, to which she requested if she could get a bottle (pointing to mine) as she was quite thirsty. Well handled by the CX gals - they got her a bottle right after take-off.