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Water Calculations for planning.

Part G water efficiency calculations for UK planning conditions and Building Regulations — the fittings-based calculation demonstrating 110 litres per person per day, prepared to the Government’s official Approved Document G methodology at design and as-built stage.

★ 5.0 Google rated Every UK local authority No advance payment
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Illustrative water efficiency calculation: house with water fittings, flow rates and the 110 litres per person per day target
Approved Document GOfficial Part G calculator methodology
110 l/person/day
Submission-ready PDF
110 l
Optional Requirement
Per person per day — G2(2)
125 l
National Baseline
Part G standard requirement
App. A
Official Methodology
The Part G water calculator
UK-wide
Full Coverage
Every local authority

What a water efficiency calculation shows

Every water fitting scored to the official methodology — WCs, showers, taps, baths and appliances — totalled against the 110 or 125 litres per person per day standard your approval depends on.

Illustrative water efficiency calculation: house with water fittings, flow rates and the 110 litres per person per day target
Illustrative visualisation — every report is prepared from your site’s actual details.
Approved Document G & the Fittings Approach

The water efficiency rules your application is judged against.

Building Regulations Part G requires every new dwelling to demonstrate limited water use. The national baseline is 125 litres per person per day — but where a planning condition applies the tighter optional requirement, your scheme must prove 110 litres per person per day using the Government’s fittings-based calculator.

When a water calculation is required

The triggers are precise — a Part G water efficiency calculation is needed where:

  • Any new dwelling is built — Building Regulations require the calculation at design stage and again as built
  • A planning condition imposes 110 l/p/d — standard across London and most water-stressed areas of southern and eastern England
  • The local plan sets a tighter target — a growing number of authorities apply stricter bespoke standards
  • A change of use creates dwellings — conversions need the same demonstration where Building Regulations apply
  • Discharging a pre-occupation condition — many consents require the as-built calculation before occupation

What your calculation must demonstrate

A compliant calculation follows the methodology in Appendix A of Approved Document G in full:

  • Every fitting scored — WCs (dual-flush effective volumes), showers, taps, baths, dishwashers and washing machines
  • The proportionate-use rules — including the bath/shower interaction rule most quick tools apply incorrectly
  • Water softeners — scored with the official ion-exchange formula where installed
  • Greywater and rainwater credits — offset calculations with their caps, where systems are specified
  • The compliance statement — the litres-per-person-per-day total against your target, signed off document-referenced
What you get

A submission-ready water efficiency statement.

Prepared for your exact fitting schedule to the current methodology, with everything building control and your case officer look for.

  • Full Approved Document G Appendix A calculation table
  • Design-stage calculation for planning conditions and building control deposit
  • As-built calculation from your installed fittings for sign-off
  • A compliant fitting schedule to buy to, where fittings are not yet chosen
  • Greywater and rainwater harvesting credits calculated where specified
  • Submission-ready PDF with a unique document reference
Illustrative water efficiency calculation: house with water fittings, flow rates and the 110 litres per person per day target
Written to the standards your local planning authority expects
Approved Document G (2024) Part G Calculator (Appendix A) 110 l/p/d Optional Requirement London Plan Policy SI 5 NPPF & PPG
How it works

From drawings to submission.

1

Send us your drawings

Email your floor plans (and fitting specification if chosen) and site address to info@clockfortress.com.

2

Get a fixed quote

We come back within 24 hours with a fixed price and a delivery date. There's no advance payment.

3

We prepare your report

Calculated to the official Approved Document G methodology and written up with the compliance statement — typically 2–3 working days.

4

Submit with confidence

Receive a planning-ready PDF, backed by our amend-or-refund guarantee if the authority rejects it.

Standards

Built on the methodology councils check for.

Every water calculation follows the Government’s national calculation methodology in full.

Approved Document G (2024 edition) The Water Efficiency Calculator for New Dwellings Regulation 36 & G2(2) — 110 l/p/d London Plan Policy SI 5 Water Infrastructure EA Water-Stressed Area Classification NPPF & Planning Practice Guidance
FAQ

Water calculations — explained.

Quick answers to the questions applicants ask us most.

Ask anything
Do I need a water efficiency calculation?
Every new dwelling in England needs one for Building Regulations — at design stage and as built. Where your planning permission carries a water efficiency condition (standard in London and water-stressed areas), the calculation must demonstrate the tighter 110 litres per person per day optional requirement rather than the 125 litre baseline.
What is the difference between 125 and 110 litres?
125 litres per person per day is the national Building Regulations baseline. 110 litres is the optional requirement councils can impose through a planning condition — it typically means specifying lower-flow showers and taps, 4/2.6-litre dual-flush WCs and water-efficient appliances. Our calculation shows exactly which fittings get you there.
What information do you need from me?
Floor plans showing kitchens, bathrooms, en-suites and utility rooms, plus your fitting specification if chosen. If fittings are not yet decided, we produce a compliant fitting schedule — maximum flow rates and volumes to buy to — so your build stays compliant without guesswork.
How are greywater and rainwater systems counted?
The official methodology credits greywater reuse and rainwater harvesting through its own contribution tables, with caps on what each can offset. Where your scheme specifies a system, we calculate the credit exactly as building control will check it.
Is an as-built calculation needed too?
Yes — Part G compliance is demonstrated twice: at design stage, then as built from the fittings actually installed, before occupation. We provide both; the as-built version is usually a same-week update of your design-stage calculation.
Which areas do you cover?
Every UK local authority. The 110-litre condition is most common across London and southern England, but the methodology is national.
Google Reviews

Rated 5.0 by our clients.

5.0★★★★★Based on 500+ Google reviews across our services
TB
Tom Barker
a month ago
★★★★★
Needed the 110 litre calculation to discharge a condition on two new houses. Fixed price, done in two days, condition discharged first time.
PS
Priya Shah
3 weeks ago
★★★★★
Our architect specified the fittings and Fortress produced the Part G calculation for building control the same week. Painless.
JW
James Whitfield
2 months ago
★★★★★
They gave us a fitting schedule to buy to before we had chosen anything — saved us swapping showers later. As-built version turned around in a day.
HC
Helen Craddock
3 months ago
★★★★★
As a planning consultant I send all my clients’ water efficiency conditions here. Accurate, quick and the councils never query them.
Get Started

Get your water calculation quoted.

Email your floor plans and we’ll send a fixed quote and timeframe — usually within 24 hours. No advance payment.

Request a quote020 3807 5825
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