What shower rating gives optimal balance between efficiency and running
cost? My current shower is an 8.5kW unit and while output is moderate it
performs reasonably well. For my new house I am thinking of fitting bigger
rated unit, 9.5 or 10.5kW. It says the bigger the wattage the greater the
flow, so in theory you cut down on the length of time the unit is on. But
surely it will use more electricity per shower? And will it not use more
water because of bigger flow rate (water at my new property is metered). I'm
getting confused - can't work out the equation between electricity cost,
water charge and comfort/efficiency. Can anyone point me in the right
direction?

Alec