Check whether the requirement applies
Approved Document G sets out the water-efficiency requirement and its application to relevant new dwellings, including specified material changes of use. Its scope should not be reduced to the statement that every bathroom refurbishment needs a whole-house water calculation. [2]
Likewise, not every alteration to the number of flats engages the requirement in the same way. Ask the designer to identify the applicable regulation and any planning condition before specifying the assessment. The type of building work matters as much as the resulting room layout. [2]
The figure is a design assessment
The litres-per-person figure is calculated from the proposed fittings and appliances under the prescribed methodology. It is not a promise about an individual household's water bill or a measurement of how long each occupant will spend showering. Approved Document G provides calculation and qualifying fittings-based routes. [2]
The specification needs to identify the actual taps, showers, WCs and relevant appliances or their declared performance. A generic note stating “water efficient” does not demonstrate that the finished dwelling meets the required limit. [2]
Coordinate the product choices
Decide the water-efficiency strategy before fixtures are ordered. If a supplier proposes a different shower or WC, ask whether the change affects the calculation and update the assessment where necessary. The designer and contractor need to coordinate changes affecting compliance rather than rely on the first issue of a schedule. [3]
Water efficiency also sits alongside the other Part G requirements, including sanitation and hot-water safety. A low flow rate is not a substitute for checking the safety and suitability of the complete installation. [1]
Completion information
Retain the assessment, final fittings schedule and relevant commissioning information. Give building control the information needed to demonstrate the applicable water-efficiency requirement, alongside the other completion documents. The calculation should describe what was installed, not an abandoned earlier specification. [2] [4]
Proposed tighter standards
Defra consulted on tighter water-efficiency requirements, and its 2026 delivery plan describes proposals including a 105-litre standard and an optional 100-litre standard. Use the operative 125/110-litre requirements until the relevant implementing provisions take effect; an announced proposal does not itself replace them. [5][6]
The Future Homes and Buildings Standards timetable should not be used as an assumed commencement date for these separate water proposals. Use the verified requirement and actual planning condition for the project, and review the specification if final regulations are published before its design is fixed. [7] [6]