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Water Calculations help you demonstrate Part G compliance – a legal precondition for Building Control sign-off on every new build.
Building Control will not issue a completion certificate for a new dwelling without a compliant Part G water calculation showing you meet the 125 litres-per-person-per-day target (or the stricter 110 l/p/d target some local authorities apply through planning conditions). The statutory requirement applies to new dwellings created by new construction – conversions and extensions sit outside it unless a specific local planning condition mandates compliance for that site. Get this wrong, or leave it too late, and the risk isn’t just a failed calculation – it’s sanitaryware that’s already been bought and fitted needing to be ripped out and replaced right before sign-off.
We design every calculation around your actual fittings rather than generic assumptions – reducing the amount of assumed data to the bare minimum so the result reflects what’s genuinely being installed. That collaborative, fittings-led approach means fewer surprises at Building Control stage, whichever target applies to your project. Learn more in our FAQ section below.
Why work with us?
Experience
Our water calculations range from single self-build and barn conversion projects through to volume new-build developments – from Autograph Homes’ five-plot development in Tickenham, North Somerset, to Cotswold Homes’ 34-plot development near Stroud, Gloucestershire, where we delivered Part G calculations spanning multiple house types alongside the wider Design SAP package. Every plot passed, with results comfortably under both the standard 125 l/p/d target and the stricter 110 l/p/d target some authorities apply.
Award-winning
Winner, Consultancy – 2025 Bristol Property Awards
Winner, Supply Chain Partner of the Year – 2025 Unlock Net Zero Awards.
Winner, Retrofit Assessor of the Year – 2023 Retrofit Academy Awards.
Highly Commended, Employer of the Year – 2023 Retrofit Academy Awards.
Speed
Project deadlines matter. We manage all data collection, modelling and reporting in-house – keeping your project moving without administrative delays.
We work to a standard two-week turnaround, with the majority of reports and certificates delivered well within that window.
Pricing
Cost depends on the scale and complexity of the project – from a single property to a large-scale portfolio.
Our rate card is reviewed regularly, so we’re confident you won’t find better value elsewhere. If you’ve found a lower quote for comparable work, let us know – we’ll match or beat it.
Support
Navigating the complexity of energy efficiency, decarbonisation and building regulation updates isn’t easy.
We’ve worked hard to explain a range of topics related to water calculations in plain English to help non-experts get the information they need.
Get Your Water Calculations Quote Today
Looking for fast and reliable Water Calculations in Bristol or nationwide?
Contact us today for a free quote and to discuss your specific project requirements.
Understanding Water Calculations: Your Questions Answered
What are Water Calculations (Part G)?
Water calculations assess a property’s predicted water use against the targets set out in Part G of the Building Regulations. The statutory requirement applies to new dwellings created by new construction, demonstrating sustainable water use before Building Control will sign off the project. Conversions and extensions aren’t automatically included, unless a specific planning condition mandates compliance for that site.
At what stage of the project should I get water calculations done?
Ideally during the design phase, before any sanitaryware is purchased. On multi-plot developments like Cotswold Homes’ 34-plot scheme near Stroud, we deliver water calculations alongside the wider Design SAP package for each house type, so fittings specifications are confirmed compliant before they’re locked into procurement – not after.
What’s the difference between the 125L and 110L targets?
The baseline Part G requirement is 125 litres per person per day. Many local planning authorities apply a stricter optional target of 110 l/p/d, usually in areas of water stress. We calculate against whichever target applies to your specific site and local authority.
Can you deliver water calculations across a large new-build development, not just a single property?
Yes – from a five-plot development for Autograph Homes in Tickenham, North Somerset, through to a 34-plot Cotswold Homes development near Stroud, where we produced Part G calculations across multiple house types as part of the wider Design SAP submission, with every plot passing comfortably under both the standard and stricter local targets.
What specific information do I need to provide for a calculation?
Floor plans, along with manufacturer specification sheets for every water-consuming fitting – WC flush volumes, basin tap flow rates, shower heads, bath capacity and washing machine/dishwasher consumption. The more accurate the fittings data, the less we need to fall back on assumed figures.
What happens if my proposed fittings exceed the water allowance?
We don’t just issue a fail – we identify specific, low-cost adjustments (aerators, flow restrictors or a different WC flush volume) that bring the calculation into compliance without requiring you to redesign the bathroom specification from scratch.
How do Water Calculations affect my EPC and Building Control sign-off?
Two ways. Building Control won’t issue a completion certificate for a new build or conversion without a compliant Part G report. Separately, the flow rates from your water calculation – particularly for hot water taps and showers – feed into your SAP assessment, so more efficient fittings can support a better EPC rating.
Who do you deliver Water Calculations for?
– Self-build homeowners
– Architects and designers managing Building Control submissions
– Volume housebuilders and developers
– Barn and property conversion projects
– Anyone extending a property where Part G applies
Need Water Calculations?
Our friendly team is ready to provide expert advice for your project. Whether you need a free consultation to discuss your options or a competitive quote for our water calculations services, we are here to help.
