Part G: Water Efficiency  Calculations

Building Compliance Testing Limited can provide you with a fast and cost effective Water Efficiency Calculations to demonstrate compliance with Part G of the Building Regulations.

compliance tickWater Efficiency Calculations

Any new build or conversion dwellings must have a water efficiency calculation completed on them. The regulations allow for a maximum of 110 or 125 litres of potable water per person per day, depending on your location. This comprises internal water use of 120 litres (per person per day) plus an allowance of 5 litres per person per day for outdoor water use. Some local authorities will set lower targets, especially in London and the South.

Non-compliance with the above may adversely affect your Standard Assessment Procedure (SAP) calculation, and therefore could result in a lower Energy Performance Certificate (EPC) rating.

The calculation considers:

– Toilets

– Taps

– Washing Machines

– Showers

– Baths

– Dishwashers

– Water Softners

– Greywater Recycling and Waste Water Recovery

The Code for Sustainable Homes Requirements

The Code for Sustainable Homes was introduced in 2007 and Part G of the Building Regulations now includes water efficiency for the first time. In addition, improved water efficiency in new developments will be backed-up through the planning system, as the Government allows the planning system to mandate water efficiency targets in excess of the Building Regulations where there is demonstrable local need.

Levels 1 and 2 have a maximum of 120 litres/person/day, levels 3 and 4 have a maximum of 105 litres/person/day and levels 5 and 6 have a maximum of 80 litres/person/day.

Calculations should be made at the design stage and again on completion. There are also credits available for meeting these targets.

Some local authorities too will set lower targets, especially in London and the South (The London Plan), in addition to other certification schemes such as WELL, LEAD and BREEAM.

Water Efficiency Calculation Process

We require a complete set of floor plans showing the number of ‘wet rooms’ such as the kitchen, utilities and bathrooms. In addition, the plans will also need to show the number of facilities which will use water, such as showers, toilets, sinks, washing machines or dishwashers.

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

A number of measures can be taken to reduce indoor water use. Flow restrictors are a convenient means to retrofit existing fittings. Low flow shower heads, low flush toilet systems or even smaller baths may be fitted. Efficient appliances, grey water and rainwater recycling can also be specified.


Let’s Talk About Your Project

Just give us a call on 01621 493594 , or email us at

Other Services

We can also offer a variety of other specialist services through our Partners, including:

– SAP Calculations

– TM52 Overheating Assessments

– U-value Modelling

– SBEM Calculations

-Energy Statements

The Compliance Package 

  • Design-stage SAP Calculation, Overheating Assessment, Air Tightness Testing, Ventilation Testing, Water Efficiency Calculation and Energy Performance Certificate

  • Reduce procurement costs, gain project efficiencies and achieve full compliance

  • One site visit, one engineer, all the expertise

  • Test results within 24-hours

Terms and Conditions Apply – Starting from £500+VAT

We’re friendly and knowledgeable bunch so why not get in touch for a chat. You can always contact Building Compliance Testing with any questions through phone, email or our online chat service.

Don’t worry, we don’t charge for advice given over the phone, so why not ask for a free quote?

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