Once you have determined each outlet’s water demand, you can combine the demands and work out exactly what your total usage would be. If you slow down your flow rate (smaller shower head) you can reduce your flow rate demand.
In very cold areas its important to choose a larger flow rate than your exact demand because the cold pipes will cool down the water and you will experience heat loss.
Room Sealled Fan Forced
You need a minimum of 16L to run a fairly HOT bath.