[Neil]

Posted as me this time.

I think it is an 8kw or 9kw shower, it is quite a few years old and was in the house when we moved in.
At setting 9, which is pretty damn hot it took 45.72 seconds to fill a 3 litre jug. so 1 litre took 45.72 / 3 = 15.24 secs.

Therefore 60 / 15.24 = 3.93 litres/minute