Water Efficiency Calculations

Water efficiency calculations predict the water consumption of a new dwelling to demonstrate compliance with Part G of the Building Regulations. As water conservation becomes increasingly important, all new builds and many conversions require these calculations. UK Building Compliance provides fast, accurate water efficiency assessments from just £10, often as part of your SAP calculations package.

What Are Water Efficiency Calculations?

Water efficiency calculations assess the projected daily water consumption of a dwelling based on the sanitaryware and water-using appliances specified in the design. The calculation considers every water outlet in the property — taps, showers, baths, WCs, washing machines, and dishwashers — and determines the total litres per person per day that the dwelling is expected to consume.

Water efficiency is measured against the targets set out in Part G of the Building Regulations. The standard requirement is that a new dwelling must not exceed 125 litres per person per day. However, some local authorities — particularly in London and the South East — impose stricter targets, often requiring consumption below 110 litres per person per day. If your project falls within the scope of the London Plan, even tighter water efficiency standards may apply.

The calculations are typically carried out at design stage as part of your SAP assessment, ensuring compliance is built into the specification from the outset. The results are presented in a formal report that can be submitted to building control or the local planning authority.

Why Do You Need Water Efficiency Calculations?

Water efficiency calculations are required by Part G of the Building Regulations for all new-build dwellings and many conversions. As the UK's population grows and water resources come under increasing pressure, ensuring new homes are designed to use water efficiently is a key part of sustainable development.

Without compliant water efficiency calculations, building control cannot sign off your project. In areas with stricter local targets, planning conditions may also require these calculations to be submitted before construction begins. Failure to meet the required targets can result in costly specification changes to sanitaryware and water-using appliances.

Getting your water efficiency calculations right at design stage is straightforward and inexpensive. By specifying water-efficient fixtures from the outset — such as dual-flush WCs, low-flow taps, and aerated showerheads — you can easily achieve the required targets while providing a comfortable living environment for occupants.

Our Water Efficiency Calculations Process

UK Building Compliance makes water efficiency calculations quick and hassle-free.

1. Information gathering — You provide a complete set of floor plans showing the number of wet rooms (kitchens, bathrooms, utilities, en-suites) and all water-using fixtures and appliances, including their flow rates and capacities where known.
2. Consumption analysis — Our team calculates the projected water consumption for each fixture based on the specified flow rates, flush volumes, and usage assumptions set out in the Part G methodology.
3. Compliance check — We verify that the total projected consumption falls within the required target (125 litres per person per day, or the stricter local target if applicable).
4. Specification advice — If the initial calculation exceeds the target, we advise on practical changes to sanitaryware specifications that will achieve compliance — such as switching to lower-flow taps or more efficient WCs.
5. Formal report — We produce a water efficiency calculations report suitable for submission to building control or your local planning authority.

What's Included

• Part G compliant water efficiency calculations
• Assessment of all water-using fixtures and appliances
• Projected consumption in litres per person per day
• Compliance verification against national or local targets
• Specification advice on achieving water efficiency targets
• Formal report for building control or planning submission
• Integration with SAP calculations package where applicable
• Reports typically completed within 5-10 working days
• Guide pricing from just £10 per dwelling

Who Needs Water Efficiency Calculations?

Water efficiency calculations are required for a range of residential construction projects:

• New-build dwellings — All new homes in England and Wales require water efficiency calculations as part of Part G compliance.
• Conversions — Many conversions creating new dwellings require water efficiency assessments, particularly where planning conditions apply.
• London Plan developments — Projects within London boroughs often face stricter water efficiency requirements that must be demonstrated through calculations.
• Planning applications — Some local authorities require water efficiency calculations to be submitted as part of the planning application, particularly in water-stressed areas.

Housebuilders, developers, architects, and self-builders all benefit from professional water efficiency calculations to ensure their projects meet the required standards.

Why Choose UK Building Compliance?

UK Building Compliance has been providing water efficiency calculations for over 15 years, delivering thousands of reports for housebuilders and developers across the UK. Our assessors hold accreditations with Elmhurst, Stroma, ATTMA, ABBE, BPEC, and UKAS.

We offer water efficiency calculations as a standalone service or as part of a comprehensive compliance package including SAP calculations, air tightness testing, ventilation testing, and EPC production. Combining services with a single provider saves time and reduces costs.

Based in Hinckley, Leicestershire, we provide nationwide coverage with competitive pricing from just £10 per dwelling. Call us on 01455 242297 for a free quote.