Water vapour from running water (not river) (5)
I believe the answer is:
steam
'water vapour' is the definition.
(I've seen this before)
'running water not river' is the wordplay.
'running water' becomes 'stream' (I've seen this before).
'not' suggests deleting specific letters.
'river' becomes 'r'.
'stream' with 'r' removed is 'STEAM'.
'from' is the link.
(Other definitions for steam that I've seen before include "letter opener?" , "get very angry" , "Mates (anag)" , "comes with a hiss?" , "Vapour from water at boiling point" .)