Notice a pipe providing isolated source of fresh water (9)
I believe the answer is:
billabong
'water' is the definition.
(I know that billabong is a type of branch)
'notice a pipe' is the wordplay.
'notice' becomes 'bill' (both can mean an advertisement).
'pipe' becomes 'bong' (I've seen this before).
'bill'+'a'+'bong'='BILLABONG'
'providing isolated source of fresh' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for billabong that I've seen before include "A stagnant pool of water in Australia" , "watercourse down under" , "Australian pool" , "Australian backwater -- no big ball (anag)" , "Australian channel" .)