Many a stream of water will put a fire out (5)
I believe the answer is:
douse
'a fire out' is the definition.
'douse' can be an answer for 'out' (thesaurus). I am unsure of the 'a fire' bit.
'many a stream of water will' is the wordplay.
'many' becomes 'd'.
'a stream of water will' becomes 'ouse' (I am not sure about this - if you are sure you should believe this answer much more).
'd'+'ouse'='DOUSE'
'put' acts as a link.
Can you help me to learn more?
(Other definitions for douse that I've seen before include "Smother with water" , "Extinguish (a fire)" , "Drench; extinguish" , "heavy blow" , "Throw water over, extinguish" .)