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

A link to the current Building Regulation can be found by clicking here. The section on Water Efficiency can be found with G2, Page 15.

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.


Part of The Compliance Package

Ensure your building meets regulatory standards with our Compliance Package. Includes air permeability tests, SAP calculations, water assessments, and ventilation testing for a fixed fee. Contact us today for peace of mind. Learn more by clicking here.

Other Services

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

SAP Calculations

Overheating Assessments

– U-value Modelling

– SBEM Calculations

– Energy Statements

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