Water consumption targets and how to reach 105 litres
The 105 litre target in London is delivered through the optional requirement in Part G of the Building Regulations, imposed by planning condition. Here is how the calculator works and which fittings actually get you there.
The 105 litres per person per day target applied to new homes in London is a mains water figure that excludes external water use. Add the standard allowance for external use and you arrive at the 110 litre optional requirement in Part G of the Building Regulations, which is the mechanism that actually delivers it. The planning system imposes the standard by condition. Building control then checks it through the water efficiency calculator.
Two documents, one number. Architects lose time when they treat the planning target and the Building Regulations requirement as separate problems.
Where the target comes from
London Plan policy on water infrastructure asks residential development to achieve mains water consumption of 105 litres or less per head per day, with a separate allowance of 5 litres for external use. Part G of the Building Regulations sets an ordinary requirement of 125 litres per person per day and makes a tighter figure of 110 litres available as an optional requirement.
The link between them is the planning condition. An optional requirement in the Building Regulations has no effect of its own: it bites only where a planning condition applied to the development requires it. So the sequence is policy, then condition, then compliance, and a scheme that is designed to 105 litres but never gets the condition will be assessed by building control against 125.
Outside London, authorities in areas of water stress apply the same optional requirement through their own local plan policies. The mechanism is identical. The policy source is different, so check the adopted plan rather than assuming the London figure applies.
The fittings and calculator approaches
Approved Document G offers two compliance routes and they are not interchangeable.
The fittings approach works from a table of maximum flow rates and volumes for each fitting type. Specify everything at or below the tabulated figure and the requirement is met. It is simple and it is set up for the 125 litre standard.
The water efficiency calculator totals estimated consumption across all the fittings in the dwelling, applying fixed use factors for frequency and duration, then divides by an assumed occupancy. It allows trade-offs: a larger bath can be offset by a lower-flow shower, and a reduced-flush WC buys headroom elsewhere. For the tighter optional requirement the calculator is the route to use.
Run the calculator early, at the stage where sanitaryware is being selected rather than after. On a flat with a single bathroom and an en suite, the margin is narrow enough that a late change of shower specification can put the dwelling over.
Specifications that reach the figure
The arithmetic is dominated by showers, baths and WCs. Taps matter less than people assume and washing machines and dishwashers are largely fixed by the appliance market.
An illustrative fittings schedule
The specification below is illustrative and must be checked against the calculator for the specific dwelling mix. It shows the shape of a scheme that reaches the tighter standard.
| Fitting | Illustrative specification |
|---|---|
| WC | dual flush, 4 litre full and 2.6 litre reduced |
| Shower | 8 litres per minute or lower, flow regulated |
| Bath | 170 litre capacity to overflow |
| Basin taps | 4 litres per minute, aerated |
| Kitchen tap | 6 litres per minute |
| Washing machine | low water use model, stated in litres per kilogram |
| Dishwasher | low water use model, stated in litres per place setting |
Three practical notes. Flow regulators need the right pressure to perform as specified, so coordinate with the hot water system rather than relying on the fitting's headline rating. A bath specified by capacity to overflow, not nominal size, is what the calculator asks for. And on dwellings with two or more bathrooms the shower specification carries most of the saving, so resist the temptation to allow a higher-flow shower in the principal en suite.
Rainwater and greywater contributions
The calculator permits a contribution from rainwater harvesting and greywater recycling within defined assumptions. Whether to use it is a judgement about whole-life cost rather than compliance.
On a small infill scheme, reaching the target on fittings alone usually costs less and carries no maintenance liability. On a larger scheme with substantial landscape irrigation, a podium garden or play space, a rainwater system can serve external demand and relieve the surface water drainage design at the same time, which makes the business case better than it first looks.
If a system is proposed, describe who maintains it, where the plant sits and how it fails safe. Reviewers have seen too many systems commissioned and then isolated. Our note on optimising site capacity under London Plan policy D3 covers how plant and amenity space compete for room on constrained London sites, which is usually where this trade-off is decided.
Non-residential water efficiency
A litres per person figure does not translate to an office, a school or a warehouse, so London policy takes a different route for non-residential buildings and looks to the water credits within the relevant environmental assessment scheme.
The practical consequence for the design team is that the water strategy has to be agreed with whoever is running the assessment, early enough to influence specification. Credits typically reward low-consumption fittings, leak detection, metering by use and sub-metering of major water-consuming plant. A BREEAM Pre-Assessment prepared at application stage should state which water credits are being targeted and what specification underpins them, and a licensed assessor is needed for the formal assessment.
Conditions securing the standard
Read the draft condition carefully before it is imposed. A well-drafted condition states the standard in litres per person per day, states whether external use is included, and requires evidence at a defined point.
Problems arise with conditions that require a standard without naming the calculation route, conditions that demand evidence before commencement when the evidence can only exist at fit-out, and conditions that reference a superseded version of the policy. All three are negotiable at the drafting stage and awkward afterwards.
Where the condition requires pre-commencement evidence, ask for it to be reworded to a pre-occupation trigger. A fittings schedule can be produced before commencement, but as-built confirmation cannot.
Evidence at application stage
The planning submission needs enough to show the target is achievable, not the final product specification. That means a statement of the standard being adopted, an outline fittings schedule or a completed calculator run for each dwelling type, a note on how the standard will be secured across the scheme, and confirmation of whether any rainwater or greywater contribution is relied upon.
Put it in the Sustainability Statement rather than scattering it across the design and access statement, and keep it consistent with the water demand figures quoted in any utilities or infrastructure section of the Energy Statement. Case officers cross-check the two more often than design teams expect.
At discharge of condition stage, supply the completed calculator output per dwelling type with the manufacturer's data sheets. That is the package that gets signed off without a second round.
This is general guidance rather than legal advice. Check the current policy wording and the current edition of Approved Document G before relying on any figure here.
Enter your postcode on PlanScope to see which documents a London residential scheme is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Where does the 105 litre figure come from?
From London Plan policy on water infrastructure, which asks residential development to achieve mains water consumption of 105 litres or less per person per day excluding external water use. With the standard allowance for external use added, that corresponds to the 110 litre optional requirement available under Part G of the Building Regulations. The two figures describe the same standard measured differently.
Does the optional requirement apply automatically?
No. The tighter standard in Part G is an optional requirement, which only applies to a development where a planning condition imposes it. Without the condition, building control will assess the scheme against the ordinary standard. That is why the planning submission and the condition wording matter as much as the specification itself.
Which compliance route should the design use?
The water efficiency calculator in Approved Document G is the route for the tighter optional standard, because the simpler fittings table is set up for the ordinary requirement. The calculator totals consumption across fittings using defined use factors, so a generous bath can be offset by low-flow taps and showers. Record the completed calculation with the fittings schedule.
Does rainwater harvesting count towards the target?
The calculator allows a contribution from rainwater and greywater systems, subject to the assumptions set out in Approved Document G. On a small scheme the cost and maintenance burden rarely justifies it, because the target is reachable on fittings alone. On larger schemes with landscape irrigation demand it is worth modelling properly.
What is expected for non-residential development?
A different mechanism. London policy looks to the water credits within the relevant environmental assessment scheme for non-residential buildings rather than to a litres per person figure, because occupancy patterns vary too much. Check the current policy wording and the scheme version your assessor will use, then specify fittings and metering to suit the credits being targeted.
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.