Reducing Waste Water
The first time you open the hot tap or your shower you have to wait some time for hot water to arrive, during that waiting time the unwanted cold or tepid water is lost to the drain, obviously this occurs because the water inside the water pipe, between the water heater and tap is cold (the deadleg).
To reduce that waste water, the length of dead leg (green) should be as short as possible, for a 22 mm pipe, every linear metre of pipe contains about 0.32 litres of cold water.
In extreme cases the dead leg could be 10 metres in length, that equates to approx. 3.2 litres of waste water every day, or 1168 litres per year wasted.
Now that might not seem to be huge amount of water, but if you multiply that by 3,000,000 households in Hong Kong, you get the idea.
In Hong Kong apartments the length of hot water dead leg pipe is typically quite short because individual water heaters are mainly used, but not always. Presently there is no legislation in Hong Kong governing the maximum length of the hot water dead leg, whereas overseas in United kingdom for example, it is specified.