Watering hole's old and unchanged (5)
I believe the answer is:
oasis
'watering hole's' is the definition.
(I've seen this before)
'old and unchanged' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' is a charade indicator (letters next to each other).
'unchanged' becomes 'asis' (I've seen this before).
'o'+'asis'='OASIS'
(Other definitions for oasis that I've seen before include "Fertile place in a desert, watering-hole" , "Fertile tract in a desert" , "Green spot; rock group" , "A place of safety or sanctuary" , "Q-and-A game" .)