What is the Part G water consumption target?

Part G requires new dwellings to achieve no more than 125 litres per person per day (or 110 L/person/day where the local authority has adopted the tighter optional standard). This is calculated using a standard methodology based on fitting specifications, not actual measured usage.

How is the 125 L/person/day target achieved?

Most effective measures: dual flush WC (4/2.6L saves ~8 L/person/day), low-flow shower head (8 l/min instead of 12 saves ~14 L), flow-restricted taps (5 l/min instead of 8 saves ~9 L), and smaller bath (140L instead of 170L).

What does the Part G calculation include?

All water-using fittings: WC flush volume, shower flow rate and duration, bath volume, basin and sink tap flow rates, and appliance usage (dishwasher, washing machine). Each is multiplied by assumed daily usage frequency per person.

Do I need water-efficient fittings in a new house?

Yes. All new dwellings must demonstrate compliance with the 125 L/person/day target through the water efficiency calculator. The calculation is submitted with the Building Regulations application. Fittings must match the specification used in the calculation.

What is the 110 L/person/day optional requirement?

Some local authorities in water-stressed areas have adopted the tighter 110 L/person/day target through local planning policy. This requires more aggressive measures: very low flush WCs, 6 l/min showers, flow-restricted taps and potentially rainwater harvesting or greywater recycling.

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Part G Water Calculator — Hot & Cold Water Requirements

Calculate water consumption per person per day from fittings specification and check compliance with Part G 125 L/person/day target.

Occupants

WC flush type

Shower flow rate

Number of baths

Basin tap flow rate

How We Calculate This

This calculator uses the Part G water efficiency methodology to estimate daily consumption per person.

Calculation method

Each fitting contributes based on flow rate/volume x assumed frequency. WC: 5 uses/day. Shower: 0.7/day x 5 min. Bath: 0.3/day. Basin: 3 uses x 1.5 min. Kitchen sink: 2 uses x 3 min.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.