Desert island with a water supply (5)
I believe the answer is:
oasis
'water supply' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'desert island with a' is the wordplay.
'desert' becomes 'os' (I can't justify this - if you can you should give a lot more credence to this answer).
'island' becomes 'is' (abbreviation).
'with' indicates putting letters inside.
'os'+'is'='osis'
'osis' placed around 'a' is 'OASIS'.
Can you help me to learn more?
(Other definitions for oasis that I've seen before include "A place of safety or sanctuary" , "Place of refreshment" , "Noel & Liam's band" , "Fertile area in desert" , "Peaceful area away from trouble" .)