Smart to get source of water decorated (4-7)
I believe the answer is:
well-dressed
'smart' is the definition.
(I've seen this before)
'get source of water decorated' is the wordplay.
'get' is a charade indicator (letters next to each other).
'source of water' becomes 'well' (water may come from a well).
'decorated' becomes 'dressed' (dressing is a kind of decorating).
'well' put next to 'dressed' is 'WELL-DRESSED'.
'to' is the link.
(Other definitions for well-dressed that I've seen before include "Smartly turned out" , "Neatly turned out" , "In stylish clothes" .)