Free to model. Building Control certificate PDF £25 +VAT (£30 inc VAT).
Runs in your browser. Toggle the target between 125 and 110 l/p/d and watch the result update.
110 vs 125 — what's the difference?
Approved Document G sets 125 l/p/d as the baseline for every new dwelling. Local planning authorities in water-stressed areas can require the tighter optional 110 l/p/d standard, usually as a planning condition. Both figures include a fixed 5 l/p/d for external use, so the fittings have to come in at 105 l/p/d for the 110 standard versus 120 l/p/d for 125.
How to pass at 110 l/p/d
It's tighter but routine: efficient taps and showers, a dual-flush WC, a sensible bath size and a flow-limited kitchen tap usually do it, and rainwater or greywater reuse can be credited. WaterMonkey shows your fittings total live, so you can adjust a flow rate or a WC and watch the number drop under the target before you commit the specification.
One dwelling type covers the estate
Building several plots to the same sanitaryware specification? One WaterMonkey calculation covers every identical plot, so a whole development doesn't need a separate calculation per house — see the main WaterMonkey calculator for multi-type schemes.
Frequently asked questions
When does the 110 litres standard apply instead of 125?
The 125 l/p/d standard in Approved Document G is the baseline for all new dwellings. The tighter optional 110 l/p/d standard applies only where a local planning authority has imposed it — usually through a planning condition in a designated water-stressed area. Always check your decision notice and conditions.
What is the fittings budget at 110 l/p/d?
Both figures include a fixed 5 l/p/d allowance for external water use, so the fittings-based part of the calculation has to come in at 105 l/p/d for the 110 standard (versus 120 l/p/d for the 125 standard). WaterMonkey shows your fittings total and the PASS/FAIL against whichever target you set, live.
How do I pass at 110 l/p/d?
It is tighter but very achievable: lower-flow taps and showers, a dual-flush WC, a smaller or efficient bath, and a flow-restricted kitchen tap usually get there. Rainwater or greywater reuse can also be credited. Model the fittings in WaterMonkey and watch the number until it passes.
Is the calculator free?
Yes — modelling the dwelling and seeing PASS/FAIL at 110 or 125 l/p/d is free in your browser. You only pay £25 +VAT (£30 inc VAT) to export the Building Control certificate PDF.
Back to the main Part G water calculator, or read what 125 l/p/d means and how the calculation reaches Building Control.