Building Control-ready PDF reports from £25 +VAT (£30 inc VAT) — covering every identical plot on the site.
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If Building Control has asked you for a "water efficiency calculation" or "Part G water calculation" for your new build, conversion or self-build — this is that, and you can do it yourself. No qualifications needed, no site visit, no survey: just the spec sheets of the taps, showers, bath and WCs you're fitting. Here's the plain-English explainer if you want the background first.
What it costs elsewhere
Online services and assessors typically charge £25–£65 for a single calculation — and again for every different house type on your site. WaterMonkey is free to use: build your fittings schedule, see PASS/FAIL live, adjust until it's right. You pay £25 +VAT only when you export the report, one fee covers every identical plot, and extra house types are £15 +VAT rather than full price. For anything beyond a single dwelling, it's not close.
What a Part G water calculation has to show
Every new dwelling must show calculated water consumption of no more than 125 litres per person per day under Part G — or 110 l/p/d where planning imposes the optional standard, which is also what a London scheme needs. WaterMonkey implements the official methodology, The Water Efficiency Calculator for New Dwellings, in full: Table 1 use factors, multiple-fittings averaging, the water softener rule, and rainwater/greywater systems to BS 8515.
Fitting by fitting
Every line behaves differently, and the differences are larger than most specifications assume — a litre per minute off the shower is worth ten times a litre off the kitchen tap. Pick the one you're about to change:
Want the whole method laid out, with a worked example from fittings schedule to final figure? The spreadsheet version, and why you don't need one.
How it works
- Enter your fittings — taps, showers, baths, WCs, white goods; pick a preset and tweak, with live PASS/FAIL as you go.
- See where the water goes — a live breakdown plus practical tips to get under target without downgrading the master shower.
- Add dwelling types — one type covers all identical plots; duplicate and adjust for each different spec, with a per-type plot schedule.
- Export when ready — a branded, Building Control-ready PDF: cover page, results table, PASS/FAIL, and a fittings page per dwelling type.
Pricing that rewards real sites
£25 +VAT (£30 inc VAT) for the report including your first dwelling type, then £15 +VAT per additional type — and a type covers every identical plot free. Typical online services charge £25–£65 per calculation, so for a mixed-type development WaterMonkey is usually the cheapest option by a wide margin. In plain numbers: forty identical plots is one £25 +VAT report; ten plots across two house types is £40 +VAT all in. Using it is free; you only pay for the PDF.
Who it's for
Developers and builders who need the water calc for Building Control sign-off; architects checking a sanitaryware spec before it's ordered; SAP assessors bundling water calcs with their assessments (shower flow rates now feed SAP 10 too). Rather we did it for you? Our Part G service has you covered.
Frequently asked questions
I'm a self-builder, not an assessor — can I really do this myself?
Yes. The calculation is a paper exercise based on your fittings' specifications — no surveys, no site visits, no special qualifications. If you can find the flow rate on a tap's spec sheet, you can do this. WaterMonkey handles all the official maths and tells you instantly whether you pass.
What do I need before I start?
The spec details of your fittings: tap and shower flow rates (litres/minute), bath capacity, WC flush volumes, and dishwasher/washing machine consumption if specified. All of it is on product spec sheets or retailer listings. Ten minutes of gathering, ten minutes of entering.
What is a Part G water calculation?
The water efficiency calculation required by Building Regulation 36 and Approved Document G for every new dwelling, using the official methodology (The Water Efficiency Calculator for New Dwellings). It must show calculated consumption of no more than 125 litres per person per day — or 110 l/p/d where a planning condition imposes the optional tighter standard.
Is WaterMonkey free to use?
Yes — building your fittings schedule, checking PASS/FAIL against 125, 110 or a custom target, and exploring what gets you under is all free in the browser. You pay only to export the Building Control-ready PDF report: £25 +VAT (£30 inc VAT), which includes your first dwelling type.
Does WaterMonkey work offline — can I install it as an app?
Yes. WaterMonkey installs on your phone or desktop like an app — use the install icon in your browser's address bar, or Add to Home Screen on iOS — and the calculator then works fully offline. Your work autosaves in this browser; you only need a connection when you export the paid PDF.
How does pricing work for multiple house types?
One dwelling type covers every identical plot on the site at no extra cost — a 40-plot site with one spec is still £25 +VAT. Each additional dwelling type (different fittings spec) is £15 +VAT. Most online services charge per calculation, so mixed-type sites cost a fraction of the usual price here.
Does it follow the official methodology?
Yes — the full DCLG Water Efficiency Calculator methodology: Table 1 use factors, Table 2 multiple-fittings averaging, the Table 3 water softener rule, and greywater/rainwater systems to BS 8515 (Tables 4.6, 5.1, 5.2 and 5.5). Results are verified against our in-house Excel masters.
Can I include rainwater or greywater harvesting?
Yes — both, using BS 8515 intermediate calculations or direct entry, with savings correctly capped against demand and protection against double-counting WC demand across the two systems.
Can I re-export after fixing a typo?
Yes — project details (project name, client, reference, plot schedule) can be changed and re-exported free for 24 hours after payment. Changing the actual fittings calculations requires a new export.
Can I get a refund if something goes wrong?
Yes — our refund practice is deliberately generous. An undelivered report refunds automatically, normally within the hour. If a report is faulty — it doesn't match your inputs or misapplies the stated methodology — we'll repair, replace or refund it under the Consumer Rights Act 2015, and minor corrections can be re-exported free for 24 hours after purchase.
Will Building Control accept the report?
It follows the official methodology (The Water Efficiency Calculator for New Dwellings) in full and shows the complete fittings schedule and working, so a building control body can check every line. Every paid report also carries a printed report ID that can be verified in seconds at energycount.co.uk/verify — and if anything raises a question, we're a real consultancy on 01202 623236, not just a website.