Toilets1 of 5

Editing specificationMake your changes, then recalculate to update your result.

Water Efficiency Calculator (Part G)

Check your new dwelling against the 125 or 110 L/person/day requirement.

No account required. Enter your proposed fittings and we’ll guide you through the calculation.

Free calculation Instant PASS / FAIL Approved Document G methodology

How would you like to calculate?Quick is designed for most users. Advanced lets you enter exact manufacturer specifications.

What are you calculating?

Please choose what you are calculating before you continue.

What you'll need

Just tell us how many toilets, taps, baths and showers the property has. We’ll apply a standard specification and the official appliance defaults for a quick Part G check.

Set up your development

Start with the development name and the Part G requirement. House types come next.

Development / site name *

You can add the site address later when preparing the Building Control reports.

Required

Part G requirement for this development

All house types will use this requirement.

Add your house types

Group together plots that use the same water specification.

Development125 L/person/day

House type

Add your first house type

Plots using the same fittings can be grouped together.

House type / name * Dwelling type * Number of bedrooms *Enter 0 for a studio.

More details (optional)

Type reference

Please specify dwelling type * Plot numbers / names *Enter all plots using this same water specification. Use a range or comma-separated list.

Your house types0 house types · 0 plots

House type saved

Do you have another house type?

All plots using the same water specification can stay grouped together.

Check your development

Make sure the house types and plots below are correct before entering the water specifications.

Development

House type 1 of 1House type

Water specification

Quick calculator

Tell us what the property has

No flow rates or flush volumes needed. We’ll use the standard quick-calculator assumptions shown below.

Quick mode assumptionsDual-flush toilet 6 / 4 L · wash-hand basins 6 L/min · kitchen/utility sinks 8 L/min · shower 10 L/min · bath 185 L · official appliance defaults.

Bedrooms *Enter 0 for a studio. Toilets (WCs) *Count the toilets in the property. Wash-hand basins * Kitchen & Utility Sinks * Showers *Enter 0 if there is no shower. Baths *If there is a shower over a bath, count 1 shower and 1 bath.

Required

Which Part G requirement applies?

Choose the maximum permitted water consumption for this dwelling.

Toilets

If all toilets are the same, enter one specification and the quantity. Add another type only when the specification differs.

What is a dual flush?

A dual-flush toilet has two flush options — usually a smaller flush for liquid waste and a larger flush for solid waste. If the toilet has two buttons or a split flush button, select Dual flush. If it only has one flush option, select Single flush.

Where do I find the flush volumes?

Use the manufacturer's full and reduced flush volumes for a dual-flush WC, or the flush volume for a single-flush WC.

Taps & sinks

Enter the manufacturer flow rate for each different fitting.

Wash-hand Basins

Where do I find the tap flow rate?

Check the manufacturer product page or technical data sheet and look for “flow rate”, normally shown in litres per minute (L/min).

Kitchen & Utility Sinks

Where do I find the flow rate?

Look for “flow rate” in L/min on the product page or technical data sheet.

Baths & showers

Tell us what is installed and we’ll only show the information that applies. If there is a shower over a bath, count both the shower and the bath.

Does the property have a bath?

Use the manufacturer's capacity to overflow in litres.

Does the property have a shower?

Use the manufacturer's flow rate in L/min.

Appliances

Don’t know the appliance specification yet? Choose “No / not yet” and we’ll use the official Approved Document G default.

Has a washing machine specification been selected?

✓ Official default will be used: 8.17 L/kg dry load.

Has a dishwasher specification been selected?

✓ Official default will be used: 1.25 L/place setting.

Anything else?

Most properties can answer No to these and continue in a few seconds.

Kitchen waste disposal unit?

Ion-exchange water softener that uses water?

Total capacity used per regeneration (%) Water consumed per regeneration (L) Average regeneration cycles per day Bedrooms served by the softener

Calculated occupancy

— occupants, using the Appendix A bedroom-based occupancy rule.

Rainwater harvesting or greywater recycling system?

Choose No if the property has neither system.

Advanced water-reuse system

Only the additional information required by the Appendix A calculation is shown.

Number of bedrooms

Occupancy is based on two occupants in the first bedroom and one in each additional bedroom; a studio is treated as two occupants.

Greywater recycling

Percentage of collected water recycled (%)

Collected from Basin / wash-hand taps Baths Showers

Used to supply WCs Washing machines

Rainwater harvesting

Collection area (m²) Yield × filter efficiency Average annual rainfall (mm/year)

Daily rainwater collection (L/day)

Used to supply WCs Washing machines

That's everything

Have a quick check, choose the requirement for the project, then we’ll calculate your result.

Required

Choose your project requirement

Select one before calculating. If Building Control or the planning documents have not specified the tighter option, the standard requirement will normally apply.

You must choose one of these two options to continue.

Review your specification

You can go back and change anything before calculating.

Next house type

How would you like to start this water specification?

Select an option, then continue.

Part G water-efficiency result

litres per person per day

Server-verified Part G calculation

Why did it fail?

These are the largest contributors in the entered specification. This does not mean a product is defective; it shows where a design change has the greatest influence on the calculation.

Ways to achieve compliance

Improve your result

You used the Quick calculator. If you apply a suggested change below, we’ll open the detailed specification so you can review the individual fixture values affecting your result. Your existing calculation will be carried across.

The options below have been recalculated against your specification. An option is only marked PASS where that change would bring the dwelling within the selected maximum.

View calculation breakdown

Water reuse contribution

Project setup

Your calculation has passed. Review the project setup below before creating the report package.

PASS

House type complete

This house type passes

Your verified specification has been completed.

PASS

Verified result

Your development0 house types · 0 plots

Saved house types

Get your Part G Water Efficiency Reports

Your calculation is complete. Add the report details below and generate the supporting documents for Building Control.

PASS only

Report details

Property address *

Dwelling type * Please specify dwelling type * Number of bedrooms *Carried across from your calculation automatically. Client / applicant Project reference Plot number / name

Development details

Development / site name * Site address

Client / applicant Project reference

Individual plot numbers and addresses are taken automatically from the house types and plots you entered above.

Your company branding (optional)

Useful for architects, consultants and developers who want the report issued in their own branding.

Company logo PNG or JPG only. The image is normalised in your browser, then sent only when you generate the secure server report.

Company name Prepared by

Company address

One final step

Complete your plot addresses

Each plot needs the address that should appear on its individual Building Control report.

0 of 0 complete

Report package

1. Water Efficiency Report Formal PASS summary for Building Control, including project details, selected requirement and final consumption.

2. Part G Calculation Schedule Full fittings/appliances schedule, component contributions, water-reuse deductions and Appendix A calculation trail.

Official report package£20.00 + VAT

One dwelling · £24.00 including VAT

Your result is free. You only pay if you want the official Building Control PDF reports. An account is created or used securely at checkout.

Individual reports Prefer separate PDFs? Download either document below.

Water Efficiency Report Main PASS report prepared for Building Control.

Part G Calculation Schedule Detailed supporting calculation and specification schedule.

Part G water-efficiency documents prepared for submission to Building Control. This is not a government-issued certificate, accreditation or approval.

Report cannot be generated yet

Amend the specification using the suggestions above, recalculate, and the PDF report will unlock once the result passes.

01 / CALCULATOR

About this water efficiency calculator

This free water efficiency calculator works out the expected water use of a new home in litres per person per day, using the method in Appendix A of Approved Document G. It is the calculation Building Control asks for under Part G of the Building Regulations, and it checks the result against the standard 125 litre limit or the optional 110 litre limit.

Choose Quick if you only know how many toilets, basins, sinks, showers and baths the home will have. We apply a standard specification and the official appliance defaults. Choose Advanced to enter exact flush volumes, flow rates and bath capacities from the manufacturers' data, or to include a water softener, greywater or rainwater system.

You see the result straight away, and it is checked a second time on our server. If the home passes, you can buy the Building Control report package from £20 + VAT. If it fails, change the fittings and recalculate as often as you like. Our guide on how to pass a failed water calculation explains which changes make the biggest difference.

02 / CALCULATOR

Looking for a water meter calculator?

This is not a water bill or water meter calculator. It estimates how much water a new home is designed to use, for Building Regulations. If you want to know whether switching to a water meter would lower your household bills, use the water meter calculator on the Consumer Council for Water website or ask your water company. New homes are normally fitted with a meter by the water company when they are connected.

COMMON QUESTIONS

Common questions

Is this a water meter calculator?

No. It is a Part G water efficiency calculator for new homes, used to show Building Control that a dwelling meets the 125 or 110 litres per person per day limit. To compare metered and unmetered water bills, use the Consumer Council for Water calculator or contact your water company.

Is the water efficiency calculator free?

Yes. The calculation and the pass or fail result are free and need no account. You only pay if you want the Building Control report package, from £20 + VAT for the first plot.

How accurate is the result?

The calculator uses the official Approved Document G Appendix A factors and appliance defaults. The result is only as accurate as the figures entered, so use the manufacturers' flow rates and flush volumes for the fittings you will install.

Can I use it for commercial buildings?

No. Part G applies to dwellings. For offices, schools, retail and other non-domestic buildings, see our commercial water efficiency calculations service, including BREEAM Wat 01.

More help: 110 vs 125 litres · what to submit to Building Control · all guides