Household water use
Bath versus shower
Which uses less water depends entirely on how long the shower is — this finds your crossover point.
Result
Your shower uses
80litres
A bath uses
85litres
Crossover point
8.5minutes
Below this, the shower uses less. Above it, the bath does.
Verdict
Your shower uses less than a bath
Method
Compares total bath volume against shower flow rate multiplied by duration, and solves for the duration at which they are equal.