A non-drinker, Dan, in hospital department, waiting on (9)
I believe the answer is:
attendant
'waiting on' is the definition.
(attending to someone)
'a non-drinker dan in hospital department' is the wordplay.
'non drinker' becomes 'tt' (abbreviation for teetotaller).
'in' means one lot of letters goes inside another.
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'dan' put inside 'ent' is 'endant'.
'a'+'tt'+'endant'='ATTENDANT'
(Other definitions for attendant that I've seen before include "Accompanying - custodian" , "One present to guide, help" , "Page, e.g." , "Assistant" , "S/he sees to the needs of others" .)