Per capita demand figures in a water supply assessment
The water efficiency figure in a planning submission is a Building Regulations standard delivered through a planning condition. Getting the route right saves an argument at occupation.
Water efficiency per capita demand appears in a planning submission for one reason: the local plan has imposed the optional technical standard of 110 litres per person per day, and the council wants to see how your dwelling will meet it. The baseline everywhere in England is 125 litres per person per day under Requirement G2 of the Building Regulations. The 110 figure is not a national rule and it does not apply unless a policy says so.
Check which applies before you specify a single tap. On a self-build plot the difference between the two standards is a handful of product choices, and on a plot where the policy quotes 105 litres the difference is nothing at all, because 105 and 110 describe the same standard measured on different bases.
Why water demand appears in a planning submission
Water efficiency is delivered through the Building Regulations, not through planning. So a planning authority that wants the tighter standard has to reach it by imposing the optional requirement through a local plan policy, and then by conditioning the permission.
That produces the slightly odd result that the planning application asks you to demonstrate compliance with a Building Regulations standard that building control will check later. Both happen. The planning submission shows the design can achieve it, and the building control submission shows the installation does.
Authorities in areas of serious water stress are the usual adopters, following the Environment Agency's classification, and some go further through their own policies. In London the figure in the London Plan is expressed as 105 litres per person per day excluding external use, which is the 110 litre standard stated on its internal basis.
Where a scheme also needs capacity confirmation from the water undertaker, that belongs in the Water Supply Assessment alongside the efficiency calculation rather than in a separate note.
The optional technical standard and how it is applied
The optional requirement is set out in the Planning Practice Guidance on optional technical standards and takes effect through the Building Regulations. It cannot be varied locally beyond the two figures the guidance provides.
Its composition matters. The 110 litre figure is 105 litres of internal use plus a fixed five litre allowance for external water. Nothing you do to the garden changes the five litres, and no policy can require less than 110 on the whole building basis.
State in your submission which figure the policy imposes, which basis you are reporting on, and what the calculation returns. Three lines. Most refusals of a water efficiency chapter come from an assessment that quotes a number with no basis attached, leaving the officer unable to tell whether it clears the policy.
Fittings based against whole building calculation
Two routes exist and they are not interchangeable.
| Fittings approach | Whole building calculation | |
|---|---|---|
| Where it comes from | The table in Approved Document G | The published water efficiency calculator |
| What it demonstrates | The 125 litre standard | Any figure, including 110 litres |
| Evidence needed | A schedule of fittings meeting the listed maxima | Flow rates, volumes and use factors for each fitting |
| Flexibility | None, each fitting must comply | Trade-offs allowed between fittings |
| Rainwater or greywater credit | Not available | Available within the methodology |
The fittings approach is simpler and it only gets you to 125 litres. For the optional requirement, use the calculator, because it lets a generous shower be offset by a small cistern and an efficient washing machine allowance.
Fill in the calculator properly. The inputs are the flow rate of each tap and shower in litres per minute, the flush volumes of each WC, the bath capacity to overflow, and the assumed consumption of the dishwasher and washing machine where these are fitted. A calculation with default appliance figures and a real shower head will not match the installed house.
Water stressed areas and tighter local policy
The Environment Agency classifies water company areas by level of water stress, and that classification is the evidence base most authorities rely on when adopting the optional requirement. Look for it in the plan's justification rather than in the policy itself.
Two practical consequences. First, an authority without an adopted policy imposing the optional requirement cannot lawfully insist on 110 litres, though officers sometimes ask. Second, a policy referring to an earlier code or to a withdrawn standard needs interpreting against the current regulations, and the safest response is to demonstrate the whole building figure and say what it is.
Where nutrient neutrality or water neutrality applies in the catchment, the efficiency figure often becomes part of a wider mitigation package, and the calculation then has to be consistent with whatever the neutrality assessment assumed. Two documents quoting different per capita figures is an easy point for an objector.
Rainwater and greywater contributions
The calculator permits a contribution from rainwater harvesting and from greywater reuse, calculated within its own methodology rather than by your own estimate of yield.
Be sceptical about relying on it. A rainwater system needs a tank, a pump, a mains backup, an annual service and a homeowner who understands it. Greywater reuse adds filtration and a maintenance regime. Both are reasonable on a scheme with a managing agent and awkward on a single self-build plot where the second owner will not know the system exists.
Reaching 110 litres with fittings alone is achievable: a 6/4 litre dual flush WC, a shower around 8 litres per minute, aerated basin taps, and a bath of modest capacity. And the bath is usually the item that decides it, because capacity to overflow is measured generously in the calculator.
Where a harvesting system is proposed for surface water reasons as well, coordinate the figure with the Drainage Strategy so the two documents agree on tank size and on what the tank is for.
Evidence the council will condition
Expect a condition in roughly this form: the dwelling shall achieve a maximum water consumption of 110 litres per person per day calculated in accordance with the published methodology, and evidence of compliance shall be submitted to and approved by the local planning authority before first occupation.
What discharges it is a completed calculation plus a fittings schedule matching what was installed, usually with product data sheets. Keep that schedule as a live document through the build. The most common failure is a late substitution of a shower or a WC by a plumber working from a different specification, discovered at occupation when the calculation no longer adds up.
As an illustrative example, a four bedroom self-build assumed at 2.8 occupants comes out comfortably under 110 litres with a 6/4 litre WC, a 7.5 litre per minute shower, 4 litre per minute basin taps and a 170 litre bath. Swap the shower for a 12 litre per minute rain head and the same house fails. One fitting.
Setting out the calculation clearly
Put four things on one page. The policy requirement and its source. The basis you are reporting on. A table of every fitting with its rate or volume. The resulting figure in litres per person per day.
Then a short paragraph confirming that the standard will be secured through the Building Regulations and that the specification will be maintained through construction. That is the whole chapter for a single dwelling, and for a larger scheme it changes only by becoming a schedule per house type.
Where a Sustainability Statement covers energy and materials as well, keep the water calculation as its own annex rather than folding it into prose, because building control will want it as a standalone document. Foul drainage capacity is a separate question again and belongs in the Foul Sewage Assessment.
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This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the standard water efficiency requirement for a new home?
Requirement G2 of the Building Regulations sets a whole building standard of 125 litres per person per day for new dwellings in England, with the detail in Approved Document G. That applies everywhere. The tighter figure of 110 litres only applies where the local planning authority has adopted a policy imposing the optional requirement.
How is the 110 litre figure made up?
It comprises 105 litres per person per day of internal use plus a fixed allowance of five litres for external water use. That matters when you read a local policy quoting 105, because the two figures describe the same standard measured differently. Say which basis you are using in the calculation so the reviewer is not left guessing.
Can I use the fittings table instead of a calculation?
The fittings approach in Approved Document G is a deemed to satisfy route for the 125 litre standard. Where a policy imposes the 110 litre optional requirement, the whole building calculation using the published water efficiency calculator is normally needed, because the fittings table does not demonstrate the tighter figure. Confirm the route with building control early.
Do rainwater harvesting and greywater reuse count?
The published calculator allows a contribution from rainwater harvesting or greywater reuse within its own methodology, so a system can help reach the target. It also brings maintenance obligations and a risk that the system is removed later. Most designers reach 110 litres with efficient fittings alone, which is cheaper and does not depend on a homeowner servicing anything.
Who checks that the standard was actually achieved?
The building control body, at the point of completion, against the specification installed. A planning condition typically requires evidence of compliance to be given to the local planning authority before occupation, which means submitting the completed calculation and the fittings schedule. Swapping a tap late in the build is the usual reason a completed calculation fails.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.