Product-led inputs
Taps, showers, WCs, baths, dishwashers and washing machines are entered using the information required by the method. We flag missing or ambiguous values.
New dwelling water use
Part G water-efficiency calculations
Check the proposed fittings as one dwelling specification and identify changes needed to meet the project target.
When you need this work
The calculation depends on the combined performance of the proposed fittings. Small specification changes can move the total, so a clear schedule matters.
We calculate estimated water consumption for the relevant dwelling design using the applicable methodology and project-specific fitting data. Where the initial specification does not meet the target, we identify which flow rates, flush volumes or capacities have the most useful effect. The final output must reflect the products intended for installation, not a nominal compliant schedule that procurement later changes. In England, the usual new-dwelling limit is 125 litres per person per day, or 110 where the optional requirement is imposed through planning. Both include the outdoor-use allowance. An eligible fittings-based route may be used instead of a whole-dwelling calculation.
What we check
Practical balancing
The lowest value is not automatically the best choice. We help the team understand how changes affect the total so it can balance user experience, product availability and the project target.
Final specification control
The calculation should be checked if key fittings change. A concise schedule gives procurement and site teams a clear reference.
Common coordination issue
A product range may include several flow rates or capacities. Use the exact tap, shower, bath, WC and appliance data, and review substitutions before purchase rather than rely on a nominal compliant schedule.
What you receive
Water calculation
The predicted consumption result using the agreed specification.
Input schedule
A traceable list of fittings and performance values used.
Option advice
Proportionate specification changes where the initial result needs improvement.
Getting started
What we need
Dwelling and target
Project location, dwelling reference and applicable water-consumption target.
Fitting schedule
Required flow rates, flush volumes, capacities and appliance consumption data.
Variations
Alternative packs, optional bathrooms or plot-specific product changes that require separate assessment.
Before commissioning
Can a generic bathroom specification be used?
Only if its performance data is defined and it accurately represents what will be installed.
What happens if products change?
Relevant changes should be checked because the combined result may move above or below the project target.
Do you choose the sanitaryware?
We can explain the performance needed, but product selection remains with the project team and supplier.
Sources and further reading
Use the edition, jurisdiction and assessment route that apply to the project. Publication of newer guidance does not automatically change an existing project’s requirements.
Check water use before procurement closes
Send the fitting schedule and target. We will confirm whether the required performance data is complete.