In some cases rainwater may be used as a means of reducing water consumption to achieve higher water efficiency performance levels.

Where rainwater is to be used, follow these instructions to calculate the contribution from rainwater (litres/person/day):


Where a communal rainwater system is to be provided supplying more than one home, this table can be used in the same way however the figures entered need to be apportioned down to an individual dwelling basis.

The above calculation is sufficient for evaluation the principles of the system in the proposed development however, for sizing of storage capacity and all other design and installation details, BS8515 should be followed.