Not taking drink on this (5)
I believe the answer is:
wagon
'not taking drink on this' is the definition.
(reference to the phrase 'off the wagon')
'not taking drink on' is the wordplay.
'not taking drink' becomes 'wag' (I can't justify this - if you can you should believe this answer much more).
'wag'+'on'='WAGON'
(Other definitions for wagon that I've seen before include "Railway freight vehicle" , "Horse-drawn vehicle" , "On this, one keeps dry!" , "Vehicle (on which abstainers travel?)" , "Transport" .)