The optional water efficiency standard and planning conditions
Part G sets 125 litres per person per day as standard and 110 as an optional requirement that only applies when a planning condition brings it into effect. Here is how that mechanism works in practice.
A water efficiency standard planning condition is the only way an English council can require a new home to use less water than the national Building Regulations figure. Part G of the Building Regulations sets a mandatory limit of 125 litres per person per day for new dwellings, and alongside it sits an optional requirement of 110 litres per person per day. That tighter figure only applies where a planning condition brings it into effect, and the council can only impose such a condition where its local plan says so on the back of evidence of water stress.
That two step mechanism, a planning condition switching on a Building Regulations requirement, is unusual and it is where most of the confusion comes from.
The national standard and the optional requirement
Requirement G2 of Schedule 1 to the Building Regulations 2010 deals with water efficiency, and Approved Document G gives the compliance routes. The default is 125 litres per person per day, calculated using the water efficiency calculator for new dwellings.
The optional requirement of 110 litres per person per day sits in the same Approved Document as an alternative standard. Both figures include an allowance of 5 litres per person per day for external water use, so the internal target under the optional requirement is effectively 105 litres.
The optional requirement is binary. A council can apply it or not apply it, and it cannot set an intermediate or a tighter figure of its own through the planning system in England. That was the point of the technical housing standards review: to stop authorities writing bespoke standards into local policy and to give housebuilders a fixed national menu.
How a council brings the requirement into play
The route runs through the local plan. National planning guidance on housing optional technical standards expects an authority to adopt a policy, supported by evidence, and then to apply the standard through a condition on individual permissions.
The condition itself is usually short: the dwellings shall be constructed to achieve a maximum water consumption of 110 litres per person per day calculated in accordance with the methodology in the Approved Document, and shall not be occupied until evidence of compliance has been provided to the local planning authority.
Where a council imposes the condition without an adopted policy behind it, the condition is vulnerable. It has to meet the usual tests of being necessary and reasonable, and a requirement applied with no evidence of local need and no policy hook fails on both. Architects picking up a draft condition list should check the plan reference before accepting it, because removing it afterwards means a section 73 application.
Evidence of water stress
The evidence base an authority needs is about the water environment, not about the development.
The Environment Agency classifies water company areas by the degree of water stress, and that classification is the starting point. Authorities also draw on the relevant water company's water resources management plan, on catchment abstraction data and on any local river or aquifer issue documented in the plan evidence.
Guidance also expects the authority to weigh the cost of the standard against development viability, and to allow a reasonable transition for schemes already designed. In practice the cost of meeting 110 litres is modest, because the specification changes are mostly to taps, showers and WCs rather than to the building fabric, and viability arguments against it rarely succeed.
Where the scheme sits in an area with genuine supply constraints, the water company's own position matters as much as the council's. A Water Supply Assessment confirming that the network can serve the development is a separate exercise from the efficiency condition, and both may be required on the same site.
Fittings based against calculation based compliance
Approved Document G offers two ways to demonstrate compliance, and the choice has real design consequences.
The fittings based approach uses a table of maximum consumption values for each fitting type. Specify everything at or below the tabulated figure and compliance follows without arithmetic. It is simple, and it is inflexible: a client who wants a rainfall shower head or a deep bath cannot have one.
The calculation approach uses the water efficiency calculator, which weights each fitting by an assumed usage pattern and produces a whole dwelling figure. That allows trade-offs, so a generous bath can be offset by low flow taps and a 4/2.6 litre dual flush WC.
| Approach | How it works | Suits |
|---|---|---|
| Fittings based | Every fitting at or below a tabulated maximum | Repeat house types, standard specifications |
| Calculation based | Weighted whole dwelling figure from the calculator | Bespoke dwellings, high specification bathrooms |
Two practical warnings. Flow rates quoted by manufacturers are often at a stated pressure, and the installed pressure may differ, so a shower rated at 8 litres per minute at 3 bar delivers more on a high pressure system unless a regulator is fitted. And greywater recycling and rainwater harvesting can be credited in the calculation, but they bring maintenance obligations that a management company has to carry for the life of the building.
Water neutrality catchments and where 110 is not enough
In a few areas the optional requirement is nowhere near the constraint.
Where Natural England has advised that development must be water neutral, because abstraction is affecting a protected habitat, new homes have to be offset so that total demand in the catchment does not rise. Schemes in those areas are typically designed to consumption figures well below 110 litres per person per day and then offset the residual through retrofitting existing properties or through an agreed credit scheme.
Nutrient neutrality works on a similar logic for a different pollutant, and the two sometimes apply to the same site. Neither is a Building Regulations matter. They are habitats regulations issues, handled through the appropriate assessment, and they can hold an otherwise acceptable scheme for a long time.
London applies its own tighter target for residential development through the London Plan, so check the current policy rather than assuming the national figure applies.
Discharging the condition
The evidence the council wants is the water efficiency calculation for each dwelling type, signed off and cross referenced to the specification.
Building control checks compliance as part of the Building Regulations process, and the planning condition usually asks for the same calculation to be sent to the planning department before occupation. Submitting the building control completion certificate on its own is often refused, because it does not show the figure.
Timing catches people. The condition is normally pre-occupation, so it can be left until late, but the specification decisions that determine compliance are made at tender. A sanitaryware substitution agreed on site in month fourteen can push a dwelling type over the figure, and the remedy at that stage is replacing fittings in completed houses.
Record the approved fittings schedule and treat changes to it the way you would treat a change to the approved drawings. The same discipline applies across sustainability evidence generally, and a Sustainability Statement that names the specification is easier to discharge than one that describes aspirations.
Where the requirement cannot be applied
The optional requirement applies to new dwellings, including dwellings formed by a material change of use, and it does not apply to non-residential buildings. Water efficiency in offices, schools and hotels is dealt with through other routes, most commonly a BREEAM credit requirement in a local policy.
It cannot be applied where the authority has no adopted policy, and it cannot be varied upwards or downwards into a bespoke local figure. A council asking for 100 litres per person per day through a condition is asking for something the regime does not provide, and that is worth saying politely at the draft condition stage rather than at appeal.
It also cannot be used to require a particular technology. A condition specifying rainwater harvesting goes beyond the standard, which is expressed as a performance figure. Where an energy or carbon condition is drafted the same way, the same objection applies, and EPC ratings in planning covers where performance based conditions do and do not bite.
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 optional water efficiency requirement?
An alternative standard in Approved Document G of 110 litres per person per day, against the mandatory 125 litres. Both figures include 5 litres per person per day for external use, so the internal target under the optional requirement is effectively 105 litres. It applies only where a planning condition imposes it.
Can a council set its own water consumption figure?
No. In England the optional requirement is binary: a council applies it or it does not. The technical housing standards regime removed the ability to write bespoke local figures, so a condition requiring 100 litres per person per day asks for something the system does not provide, and is worth challenging at draft condition stage.
What evidence does a council need before imposing it?
An adopted local plan policy supported by evidence of water stress, typically drawing on the Environment Agency's classification of water company areas, the water company's resources management plan and local catchment data. Guidance also expects the authority to weigh the cost against viability and allow a transition period.
Should I use the fittings approach or the calculator?
The fittings approach specifies every fitting at or below a tabulated maximum and needs no arithmetic, which suits repeat house types. The calculator weights each fitting by assumed usage and gives a whole dwelling figure, allowing a generous bath to be offset elsewhere. Bespoke dwellings almost always need the calculation route.
How is the condition discharged?
By supplying the water efficiency calculation for each dwelling type, cross referenced to the specification. A building control completion certificate on its own is usually refused because it does not show the figure. Keep the approved fittings schedule under change control, since a late sanitaryware substitution can push a house type over the limit.
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.