Painter of British water? (5)
I believe the answer is:
blake
'painter' is the definition.
(William Blake)
'british water?' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'water?' becomes 'lake' (lake is a kind of water**).
'b'+'lake'='BLAKE'
'of' acts as a link.
(Other definitions for blake that I've seen before include "William -, (Jerusalem)" , "William -, English poet, artist and visionary" , "Exposed (to the air)" , "artistic poet" , "Songs of Innocence poet" .)