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105 or 110? Both, and they agree
London Plan Policy SI 5 asks development proposals to achieve mains water consumption of 105 litres or less per person per day, excluding an allowance of up to five litres for external water consumption. Nationally, the tighter optional standard under Approved Document G is 110 l/p/d — and that figure includes a fixed 5 l/p/d of external use, because the Part G methodology adds it at the end of the calculation.
So the two numbers describe the same dwelling. 105 excluding external plus the 5 litre allowance is 110 including it. If your planning condition says 105 and your calculation says 110, nothing has gone wrong. Full detail on the tighter standard is on the 110 l/p/d calculator page.
Don't confuse it with the proposed national 105. Defra has consulted on cutting the England-wide standard from 125 to 105 l/p/d. That figure includes external use, so it is a genuinely tighter number than the London one — and it is not in force. Today, a London scheme is designed to 110 on the calculator.
What to put on the submission
Run the calculation normally and report the figure it produces, external allowance included. Then say so, in one line, on the face of the document: "110 l/p/d including the 5 l/p/d external allowance, equivalent to 105 l/p/d excluding external use as required by London Plan Policy SI 5."
It takes a sentence and removes the single most common query on a London water submission — a planning officer holding a policy that says 105 and a compliance document that says 110, with nothing on either explaining that they match. The same calculation serves both the planning water statement and the Building Control file, so there is no reason for the two to carry different-looking answers.
Boroughs that go further
The London Plan is the floor, not the ceiling. Boroughs set their own Local Plan policies, and some are moving tighter: Hammersmith & Fulham's emerging Local Plan, at Regulation 18 consultation stage, proposes a target of no more than 95 l/p/d for internal use plus the 5 litre external allowance — which is 100 l/p/d on the Part G calculation.
Emerging policy is not adopted policy, and it may change before it is. But it makes the practical point: the number that binds your scheme is in your decision notice and your borough's Local Plan, not in a general article about London. Read those first, then set the calculator to whatever they say — WaterMonkey takes a custom target as readily as 125 or 110.
Getting from an ordinary spec to 110
An unremarkable modern specification lands at about 123.9 l/p/d, so a London scheme needs to find roughly 14 litres. Three ordinary changes usually cover it — the shower from 10 to 8 l/min, the WC from 6/4 to 4.5/3 and the basin taps from 6 to 5 l/min — with no change to the layout and no downgrade to the master shower. Flats, which often have a shower and no bath, usually start lower still.
Where a scheme cannot get there on fittings alone, rainwater and greywater reuse can be credited against WC demand, and the calculator handles both — including the guard against counting the same demand twice.
Rather hand it over?
We run Part G water calculations as a desktop service for London schemes — send the sanitaryware schedule, or the drawings if the fittings aren't picked, and the calculation and compliance report come back ready for the file. If the scheme fails at 110, you get the options to fix it in the same email.
Frequently asked questions
What water efficiency standard applies in London?
London Plan Policy SI 5 asks development proposals to achieve mains water consumption of 105 litres or less per person per day, excluding an allowance of up to five litres for external water consumption. Individual boroughs apply it through their own Local Plan policies, and some are consulting on going tighter still, so check the policy for your borough as well as the London Plan.
Is the London 105 l/p/d the same as the national 110 l/p/d?
Yes, for calculation purposes. The London figure excludes external water use; the Part G methodology adds a fixed 5 l/p/d of external use at the end of the calculation. So 105 excluding external and 110 including external describe the same specification. Set the calculator to 110 and a London scheme is satisfied.
Which number do I put on the calculation?
Run the Part G calculation as normal and report the figure it produces, which includes the 5 l/p/d external allowance — so a compliant London scheme shows about 110 or below. State the convention on the submission, so a 105 in the planning file and a 110 in the Building Control file are visibly the same calculation rather than two different answers.
Do any London boroughs require less than 105?
Some are consulting on it. Hammersmith & Fulham’s emerging Local Plan, at Regulation 18 stage, proposes a target of no more than 95 litres per person per day for internal use plus a 5 litre external allowance — 100 l/p/d on the Part G calculator. Emerging policy is not adopted policy, but it shows the direction, and borough requirements vary, so read the decision notice and the Local Plan rather than assuming the London Plan figure.
Is the calculator free?
Yes. Building the fittings schedule and seeing live PASS/FAIL against 125, 110 or a custom target is free in your browser, with no sign-up. You only pay £25 +VAT (£30 inc VAT) to export the Building Control-ready PDF, and one dwelling type covers every identical plot.
Back to the main Part G water calculator, or read what 125 l/p/d means, the 110 l/p/d planning condition and how the calculation reaches Building Control.