Flowing water to be hot (4)
I believe the answer is:
burn
I believe this is a double definition.
'flowing water' is the first definition.
(Scottish term for a stream)
'to be hot' is the second definition.
(something which burns is very hot)
(Other definitions for burn that I've seen before include "Char" , "Heat injury; stream" , "Set on fire" , "Use heat < in attempt to eliminate" , "Copy (a CD)" .)