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Water Efficiency Calculations

As of 6th April 2010 all new homes and conversions are required to meet new water performance targets. Building Control will be asking for calculations to demonstrate that in all new developments and conversions no more than 125 litres of potable water are used per person/per day. Part G of The Building Regulations states that ‘Reasonable provision must be made by the installation of fittings and fixed appliances that use water efficiently for the prevention of undue consumption of water.’

Water is a resource that is going to come under increased demand as the population of the UK expands, therefore it must be used efficiently. In some areas, especially in London and the South, targets may be set to be lower e.g. 105 or even 80 litres per person/per day.

Maximum consumption of potable water (litres/person/day):

  • Code for Sustainable Homes (Level 1/2) 120 litres/person/day
  • Code for Sustainable Homes (Level 3/4) 105 litres/person/day
  • Code for Sustainable Homes (Level 5/6) 80 litres/person/day

Some larger sites require a full water reduction strategy as part of the planning process. This is a more detailed report demonstrating the water efficiency measures to be utilised on a site wide basis.

There are a range of factors that need to be considered in water efficiency calculations. These include:

  • Bath capacity
  • Shower’s and tap’s flow rates
  • The flushing/cistern capacity of the toilet
  • Dishwasher consumption
  • Washing machines consumption per cycle
  • Water softener
  • Rain harvesting technologies

It is important to address issues surrounding water efficiency at the planning stage of any project. This will help you to identify and implement some of the most cost effective methods of minimising water consumption and achieving the required levels of compliance.

Outside of water calculations being specifically requested in the building regulations, it’s important that we all consider our impact on the environment. By ensuring that your development complies with the maximum limit of 125 litres of potable water per person per day, you are also ensuring that you’re not contributing to excess water use. Ethical reasons aside, using fittings with low flow-rates and capacities could mean you also make significant savings on your water bill.

If you are unsure about whether your property needs this assessment, please contact us today for professional advice. QuinnRoss Energy will use our BRE approved Part G water efficiency calculation tools to demonstrate your compliance.

What’s a water efficiency calculation?

This is a calculation that predicts annual water use for a dwelling based on the components in it, i.e. toilets, taps, showers, washing machines, dishwashers.

Are they important?

Yes. It is a legal requirement for all new dwellings to show they are reducing their water consumption as much as possible. If you don’t do it, you won't get Building Regulations signed off.

Need Help With Your Project?

Contact one of our energy assessors today on 01795 845 780, or email us at hello@quinnross.energy


RIBA stages

When do I need Water Efficiency Calculations?

Services for RIBA 0 - 7

Whether you need a SAP for a bungalow, or overheating analysis for a penthouse, our technical specialists will work with you to find the best solutions for compliance within your deadlines and budget, explaining them in plain English.