A bit of magnificent hard water! (3)
I believe the answer is:
ice
'hard water' is the definition.
(I've seen this in another clue)
'a bit of magnificent' is the wordplay.
'a bit of' indicates a hidden word.
'ICE' is hidden within 'magnificent'.
(Other definitions for ice that I've seen before include "Diamond" , "Cool down" , "kill American" , "Frozen water; kill (slang)" , "Rocks on which drink is served?" .)