In all fairness, nothing but hard water (7)
I believe the answer is:
justice
'in all fairness' is the definition.
'Justice' can be an answer for 'fairness' (I've seen this before). I am not certain of the 'in all' bit.
'nothing but hard water' is the wordplay.
'nothing but' becomes 'just' (both can mean simply or merely).
'hard water' becomes 'ice' (I've seen this in another clue).
'just'+'ice'='JUSTICE'
Can you help me to learn more?
(Other definitions for justice that I've seen before include "Judge, magistrate" , "Courts' function" , "It's dispensed over the bar" , "Fair play" , "Equity" .)