Conflict about the empty lake’s contents (5)
I believe the answer is:
water
'lake's contents' is the definition.
(lakes are made up of water)
'conflict about the empty' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'about' means one lot of letters goes inside another.
'empty' says to hollow out the word (remove centre letters).
'the' with its centre removed is 'te'.
'war' placed around 'te' is 'WATER'.
(Other definitions for water that I've seen before include "Common fluid" , "What can produce solution" , "What makes the Somme" , "Basic liquid" , "Superior's full of it" .)