Part G Water Efficiency Calculations

What is a water calculation?

Current building regulations (Part G) require a maximum water usage of 125 litres per person per day using the governments standard water usage factors.

Using project drawings and specifications we will undertake a desktop appraisal of the dwelling and water usage fittings within. These will include, basins, toilets, showers, baths, washing machines, dishwasher, water softeners, waste disposal units, grey and rain water recycling systems.


Once our team of assessors have calculated the usage based on the design drawings and specification they will provide a report for each dwelling. This is will be required by your building control officer , warranty or NHBC for final certification. However, don’t leave it until the end of the project to comply, as replacing any fixtures or fittings can be needlessly expensive.

combine your water calculation with

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What are the requirements?

For new build properties the maximum allowable for water usage is 125 litres per person per day. However many planning authorities require this to be lower in an effort to help with reducing overall water consumption and demand on the main water supplies. Below is a guide to some common requirements:-

Common Requirements
Internal Usage
External Usage
Total Usage
Building Regulations (Part G2)
Equivalent Code Level 1/2
Equivalent Code Level 3/4
Equivalent Code Level 5/6

Water calculations explained?

Want to know more about water efficency, get the complete low down on the why, how and what. To learn more click here and see our water calculation explained guide.

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How we can help?

Using our years of expertise we are able to advise on the size, flow rates, capacities and quantities for any size project. We typically assist in either of the following stages:

Pre Planning

If you are making a planning submission for a new dwelling or site, you may be asked by the local planning authority to submit evidence of the predicted water usage. At this stage you are unlike to know the exact specifications for all the water usage fixtures and fittings. To help at this early stage of the project we are able to conduct a review of the dwelling/s and provide a detailed specification of maximum flow rates/capacities of the water fixtures in order to demonstrate the desired water efficiency usage set by that particular planning authority. You will be provided with a PDF report which can be used to submit with your planning application.

Post Planning (pre-commencement conditions)

Depending whether you submitted evidence of the water usage at a pre-planning stage, you may well have secured planning but have a pre-commencement condition to discharge before you can start the building works. If you didn't submit the predicted water usage with your application we can assist in the same way as above and provide you with a detailed report confirming the maximum flow rates/capacities of the water fixtures in order to demonstrate the desired water efficiency usage set by that particular planning authority. You will be provided with a PDF report which can be used to submit for discharge of the pre-commencement condition.

Pre or Post Planning (a detailed review)

We are able to undertake a full review of the proposed fixtures and fittings to be installed/provided to ensure these are sufficiently compliant with your particular requirements and the flow rates/capacities of the water fixtures are allowable. If for what even reason any of the fixtures or fittings exceed the requirements we'll provide helpful and practical advice and solutions. Upon completion of the calculation you will be provided with a PDF report which can be used to submission to the planning authority or building control body for approval.

Why Use BEAT?

BEAT Solutions are experienced in produced Part G Water Efficiency Calculations having worked on hundreds of projects and thousands of dwellings. These level of experiences enables us to offer years of product knowledge and helps ensure a desirable outcome for project.

Very professional advice, friendly prompt service. Quick delivery of all certificates needed to complete building project.

B Foster - Farnham

When should I have my air test?

The air test should be conducted once all the building works are complete, this includes painting, decorating and floor coverings. Don't rush and get your air test too early. This increases the likelihood of a failure. We have a saying here at BEAT Solutions to establish whether the building is fit for testing. "would you let a paying customer move in yet?" If you can answer yes to this simple question, then it's is likely the building is ready.

How long quickly to i get my result and certificate?

The air test result is calculated onsite and for all air tests completed before 4pm we issue the certificate the same day via email.

What do we need to undertake an air test?

We require drawings including floor plans, sections, elevations and site plan to enable us to calculate the buildings envelope area. Additionally we'll require a copy of the design stage SAP calculation to establish the assumed air permeability score.

What happens if my air test score is too high and fails?

We are focused on helping all projects succeed. Therefore if your test fails we'll identify the areas that are leaking using the latest diagnostic equipment and techniques. We'll then allow yon upto 30 minutes remedial time to resolve the problematic areas and will re-test again for FREE. This is usually sufficient for most projects to achieve the required pass result. If for whatever reason the remedial works aren't to be completed during our visit, then a separate rechargeable retest will be required.

How to i get a quote?

Just send us your project drawings via email to or use our quote request form and we'll send you an electronic quote by return.

How long does an air test take?

Depending on the size of the building the following can be used as a guide:- Small house or flat = upto 1.5hrs Large House = upto 2hrs Small commercial units i.e office, shop = upto 2hrs Medium commercial units i.e carehome, school = upto 4hrs Large commercial units i.e office blocks, hotels = upto 6hrs

Can you test multiple plots or units on the sameday?

Yes, generally as a guide we can test upto 10 plots in a single visit. For large volume projects we can test over multiple days if required.

What about my extractor fans and trickle vents?

The purpose of the test is to measure the amount of uncontrolled air movement. Therefore you are required to temporarily seal all extract ventilation fans including whole house ventilation systems. Also all trickle vents are closed, these can be temporarily sealed by the customer if you'd prefer. For further guidance on preparing for an air test see our site readiness checklist.

Frequently Asked Questions