Busy worker going to river for a drink (4)
I believe the answer is:
beer
'for a drink' is the definition.
(beer is a kind of drink)
'busy worker going to river' is the wordplay.
'busy worker' becomes 'bee' (I've seen this in another clue).
'going to' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation).
'bee'+'r'='BEER'
(Other definitions for beer that I've seen before include "See 4 down" , "pint" , "Hop drink" , "Drink brewed with malt" , "Perhaps bitter" .)