Water efficiency standards and how planning secures them
The optional technical standard only applies where local policy justifies it. Here is how the fittings calculation works and how compliance is actually verified.
A water efficiency planning condition in England does one thing: it applies the optional technical standard of 110 litres per person per day to new dwellings, in place of the 125 litres per person per day baseline in Part G of the Building Regulations. The condition itself is short. What sits behind it is a fittings-based calculation, a local plan policy that has to be justified by evidence of water stress, and a verification step that happens through building control rather than through planning.
Developers often treat the standard as a box to tick at the end. It is a specification decision, and on a scheme with high-flow showers already specified it can mean changing the sanitaryware package after contracts are let.
The optional technical standard and how it is adopted
The optional standard is not automatic. Planning Practice Guidance on housing optional technical standards is clear that an authority may only apply it where there is a clear local need, justified through the local plan and supported by evidence, and where the impact on viability has been considered.
So the first question on any site is whether the adopted plan contains the policy. If it does not, an officer asking for 110 litres per person per day is asking for something the plan does not support, and that is worth a polite conversation rather than silent compliance.
Where the policy exists, it is applied by condition on the planning permission. The condition is the trigger that brings the tighter requirement into the Building Regulations regime. The basics of that mechanism are set out in the optional water efficiency standard and planning conditions.
Calculating consumption by the fittings approach
The calculation uses the water efficiency calculator methodology that sits with Approved Document G. Each fitting is assigned a flow rate or a volume, multiplied by an assumed use factor, and summed to give a whole dwelling consumption figure per person per day. A fixed allowance for outdoor use is added on top.
The fittings that move the number most are the shower, the WC and the taps. A single high-flow shower head can consume more than the rest of the dwelling's fittings combined, which is why the calculation usually resolves into a decision about shower flow rate.
| Fitting | Where the savings come from | Practical constraint |
|---|---|---|
| Shower | Flow rate in litres per minute | Perceived performance and pressure |
| WC | Dual flush effective volume | Drainage run gradients on low-flush systems |
| Taps | Flow rate at the basin and sink | Kitchen taps used for filling containers |
| Bath | Capacity to overflow | Marketing expectations for family housing |
| Washing machine and dishwasher | Assumed standard values | Not usually specified by the developer |
Run the calculation early, at the point the sanitaryware specification is being chosen rather than at condition discharge. Retrofitting compliance means substituting fittings that the buyer has already seen in a show home.
How the standard is imposed and evidenced
The usual condition requires the dwellings to be constructed to achieve water consumption of no more than 110 litres per person per day, with evidence submitted before occupation. Some authorities ask for the calculation at the discharge stage. Others rely on the building control process.
That division causes confusion. Once the condition applies the optional requirement, compliance is a Building Regulations matter, and building control checks the fittings schedule against the calculation. The planning condition establishes that the tighter standard applies. It does not create a separate verification regime, and authorities that ask for post-occupation evidence beyond the building control position are usually asking for more than the mechanism provides.
Read the condition wording and, if it duplicates building control, ask for it to be reworded before permission is issued rather than arguing at discharge.
Conditions, timing and the discharge trail
The timing of the condition matters as much as the wording. A condition requiring the calculation to be approved before work starts will hold up groundworks over a sanitaryware schedule, which serves nobody, and officers will usually agree to move it to a pre-occupation trigger if asked at the right moment.
Keep the paperwork together. The calculation, the fittings schedule with model references, and the building control confirmation form a single trail, and a purchaser's solicitor will ask for it years later when the property is sold.
Where a scheme is built in phases, discharge the condition phase by phase rather than for the whole site. A single discharge covering 200 units locks the specification for four years of construction, through at least one change of supplier.
Water and nutrient neutrality catchments
In a small number of areas the water question goes well beyond the optional standard. Where advice from Natural England has identified that abstraction affects a protected habitat, new development may need to demonstrate water neutrality, meaning no increase in overall water use across the affected area.
In those areas 110 litres per person per day is a starting point rather than an answer, and schemes typically have to reach lower consumption figures and then offset the residual through retrofit programmes or other mitigation. The evidence expectations are set out in what applicants must show on water neutrality.
Nutrient neutrality operates on the wastewater side and is a different calculation with different mitigation, though the two often appear together in the same catchment. A Water Supply Assessment is the usual place to bring the supply-side evidence together.
These designations are advice-led and change. Confirm whether one applies at the point of submission.
Rainwater and greywater reuse in the calculation
The calculator allows a deduction where rainwater harvesting or greywater recycling is installed, subject to the system being properly specified. On paper this is an attractive route to a low figure.
In practice it carries maintenance liability and long-term performance risk. A rainwater system with a failed pump reverts to mains supply, and nobody reports it. Authorities are increasingly wary of schemes that meet the standard only through reuse, and reviewers will ask how the system is maintained and who pays.
Use reuse where there is a genuine demand for non-potable water, such as landscape irrigation on a larger scheme, and meet the fittings target on its own where possible. A dwelling that complies through fittings alone complies for its whole life.
Where local policy goes further
Some authorities set more demanding figures in their own plans, particularly in London and in water-stressed parts of the south and east. Where that happens, the policy has to be justified in the same way, and the applicant should check whether the evidence base supports the number being applied.
The commitment usually appears in the Sustainability Statement alongside the energy case, and the two should be consistent. A scheme claiming a high sustainability standard while specifying the maximum permitted shower flow reads badly.
And say what you are actually doing. A statement that gives the calculated figure, lists the fittings assumed and names the person responsible for holding the specification through procurement is worth more than a paragraph of intent.
Enter your postcode on PlanScope to see which water and sustainability reports your site is likely to need.
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
Is the 110 litre standard automatic for new homes?
No. Part G of the Building Regulations sets a baseline of 125 litres per person per day. The tighter optional standard of 110 litres applies only where the local plan contains a policy justified by evidence of local water need, and only when a planning condition imposes it on the particular permission.
How is water consumption calculated?
Using the water efficiency calculator methodology associated with Approved Document G. Each fitting is given a flow rate or volume, multiplied by an assumed use factor and summed to give litres per person per day, with a fixed allowance added for outdoor use. Shower flow rate and WC flush volume usually decide the result.
Who checks that the standard has been met?
Building control. Once a planning condition applies the optional requirement, compliance sits within the Building Regulations regime and is checked against the fittings schedule. The planning condition establishes that the tighter standard applies rather than creating a separate verification process, so watch for conditions that duplicate the building control check.
Can rainwater harvesting be counted?
Yes, the calculator allows a deduction for properly specified rainwater harvesting or greywater recycling. Authorities are cautious about schemes that only comply through reuse, because a failed pump reverts the dwelling to mains supply without anyone noticing. Meeting the target through fittings alone gives lifetime compliance without maintenance dependency.
What is different in a water neutrality area?
Development must not increase overall water use across the affected area, so 110 litres per person per day becomes a starting point rather than the answer. Schemes usually have to reach a lower figure and then offset the residual demand through retrofit or other mitigation, evidenced before permission rather than by condition.
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.