A: A minimum of 50 galls (approx 225lts) is recommended howeveryou may need more or less depending on the flow rate of your shower (if youhave body jets etc. You will use more water) if you have good pressure at theball valve and the tank makes up quickly then you could manage with less.
For example a 10min shower using 15lts per min =150lts.
Answered 130 days ago | The doc