Uselessness of water company for one after onset of freeze (8)
I believe the answer is:
futility
'uselessness' is the definition.
(futility is a kind of uselessness)
'water company for one after onset of freeze' is the wordplay.
'water company for one' becomes 'utility' (water company is a kind of utility).
'after' means one lot of letters go next to another.
'onset of' suggests taking the first letters.
The first letter of 'freeze' is 'f'.
'utility' put after 'f' is 'FUTILITY'.
'of' acts as a link.
(Other definitions for futility that I've seen before include "Uselessness" , "Pointlessness" , "No prospect of success" .)