What is water flow rate? This is how much water per minute will be release by either your tap, mixer or shower-head? You can calculate this by doing the bucket test.
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.
Diaphram activated
Low pressure
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.
Constant Temperature
Room Sealled Fan Forced
You need a minimum of 16L to run a fairly HOT bath.