Preserve hot water? (3)
I believe the answer is:
jam
I believe this clue is a double definition.
'preserve' is the first definition.
(jam is a kind of preserve)
'hot water?' is the second definition.
(thesaurus)
(Other definitions for jam that I've seen before include "Spread; improvise (jazz)" , "Conserve" , "Preserve - predicament" , "Sweet stuff for bread - stuff it in" , "Block signals" .)