Whilst water is a renewable resource, many areas of the UK are under water stress. Even for areas where water supply is plentiful, the energy to supply potable water, and treat the resulting wastewater is often raised as an environmental concern.
In practice the energy used to heat water in the home is around seven times greater than this. For domestic buildings achieving Passivhaus levels of thermal performance, the energy required to heat hot water is greater than for space heating. For these reasons, the AECB Water Standards prioritise hot water savings.
The AECB standards are based on performance requirements for individual water-using devices rather than a whole building calculation method, which tends to encourage game playing with credits being awarded for fittings that can be easily changed. The whole building calculation approach also allows cold-water savings to offset increased hot water use.
Read more on AECB's Water Standard here.