Froggy, sorry I can't let that point re the hot water system go by.
Will save you power but at what cost??...A bit like the electric car...Sorry I digress
That is a typical example of what looks like the right thing to do BUT ISN'T.
DO NOT reduce your hot water system to 50 deg cel. it is possible for bacteria like legionnaires to grow.
In fact it is State law that the hot water service by set at 60 deg Cel.
You then have a tempering valve to allow cool water to mix with your hot to get the desired maximum temperature (ie 50 deg if so desired).
Tempering valves
In hot water storage systems for residential buildings, hot water must be heated to a minimum of 60° Celsius to prevent the growth of bacteria such as Legionella.
A tempering device ensures that hot water is delivered to taps at a maximum 50° Celsius. This temperature is considered sufficient for domestic hygiene purposes and effectively reduces the risk of scalding-related injuries from hot water use.
A tempering device is required to be fitted to all new and replacement hot water systems.
http://www.hpw.qld.gov.au/construct.../Pages/ElectricHotWaterSystemReplacement.aspx
