Drop of ouzo when one's in watering hole (5)
I believe the answer is:
oasis
'watering hole' is the definition.
(I've seen this before)
'drop of ouzo when one's' is the wordplay.
'drop of' indicates taking the first letters.
'when' becomes 'as'.
'one's' becomes 'is' (Roman numeral).
The initial letter of 'ouzo' is 'o'.
'o'+'as'+'is'='OASIS'
'in' is the link.
(Other definitions for oasis that I've seen before include "English rock group in the desert" , "A place of safety or sanctuary" , "Fertile area in desert" , "Desert refuge" , "Green spot; rock group" .)