Fake non-drinker has nothing but a high voice (8)
I believe the answer is:
falsetto
'a high voice' is the definition.
(I've seen this before)
'fake non-drinker has nothing' is the wordplay.
'fake' becomes 'false' (synonyms).
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'has' is a charade indicator (letters next to each other).
'nothing' becomes 'O' (O resembles 0).
'false'+'tt'+'o'='FALSETTO'
'but' acts as a link.
(Other definitions for falsetto that I've seen before include "Flat toes (anag.)" , "High singing method" , "Let fatso have voice above natural range" , "Note production" , "Unnatural voice" .)