No confidence water vapour leads to corrosion (8)
I believe the answer is:
mistrust
'no confidence' is the definition.
'water vapour leads to corrosion' is the wordplay.
'water vapour' becomes 'mist'.
'leads' says to put letters next to each other.
'to corrosion' becomes 'rust' (rust is a kind of corrosion).
'mist'+'rust'='MISTRUST'
(Other definitions for mistrust that I've seen before include "Regard with suspicion" , "Have doubts about" , "Suspect (someone)" , "reservations" , "Have no confidence in (someone)" .)