The Government updated Part G of the Building Regulations in April 2010. This sets a whole building standard of 125 litres per person per day for domestic buildings. This figure can be less for ‘Code for Sustainable Homes’ dwellings.
The calculation method requires the use of water consumption figures provided by manufacturers product details (key features such as flow-rates, toilet flush volumes and dishwasher litres / place settings). The estimated water usage must be calculated in accordance with the published methodology set out in the ‘The Water Efficiency Calculator for New Dwellings’.
The exercise is a very simple form that looks like this: