Introduction
Up until the early 20th century women everywhere slaved over open cauldrons heating water for baths and clothes washing. Then in 1917 a woman, Ida Forbes invented the electric hot water cylinder. The design has proven to be robust and reliable through time and has become the “gold standard ” against which all other hot water systems are measured because of its widespread use. The main benefit to us is the entirely automated approach to hot water.

When planning a hot water system a change in thinking is desirable with energy efficiency being the first consideration. There is no one solution that is best and economics play a conflicting role in choices made. The objective is to analyse and understand the role that a well-designed hot water system can play in reducing energy consumption.

• Modern appliances such as the dishwasher and washing machine heat their own water very efficiently. Therefore hot water pipe runs to them should no longer be considered an essential element of the design.
• Where high flow rates are available, a low flow showerhead will reduce hot water consumption to around 8 – 10 Litres Per Minute (LPM). Although it will make little difference to the energy bills of single household consumers it will make a significant difference to high usage households.
• Small single faucet tankless systems may be desirable for low use areas such as the kitchen sink, laundry tub, and vanity and toilet hand basin fixtures.
• High use facilities such as baths and showers require a different approach since they are the main consumers of hot water. Benefits can be gained for showers in particular by using wastewater heat recovery systems in their cold water supply. These raise the cold water temperature by several degrees resulting in substantially lower hot water consumption.
• Solar hot water should be considered as a part of any hot water system.