The requirement
Part G of the Building Regulations caps the calculated water consumption of a new dwelling at 125 litres per person per day (some planning conditions impose a tighter 110 l/p/d optional standard). The calculation uses the water efficiency methodology, based on the flow rates and capacities of the fittings you specify: taps, showers, baths, WCs, white goods.
When it gets tricky
125 l/p/d is comfortable with modern sanitaryware — but large baths and powerful showers can push you over. The fix is offsetting: low-flow fittings elsewhere, dual-flush WCs, or alternative water sources such as rainwater or greywater harvesting. We’ll tell you the cheapest combination that works for your spec rather than asking you to downgrade the master shower.
Prefer to run the numbers yourself?
Our free in-browser calculator, WaterMonkey, runs the full official methodology with live PASS/FAIL at 125 or 110 l/p/d — model your fittings for free, and the Building Control-ready PDF is just £25 +VAT when you need it.
Open the free Part G calculator →Beyond Building Control
We also produce water calculations for planning and other purposes — legacy CSH level 4, the G2 optional requirement, and regulation 36 notices. Since SAP 10 now uses shower flow rates too, it pays to have one assessor doing both calculations with consistent fittings data — see our Compliance Pack.
Send us your sanitaryware schedule — get a quote or call 01202 623236.