What This Requirement Covers
Approved Document G2 requires new dwellings to achieve a maximum water consumption of 125 litres per person per day (l/p/d), or 110 l/p/d where required by planning conditions. Meeting these targets requires careful selection of water-using fixtures and fittings.
Key Requirements
Water Efficiency Calculator
The Part G water efficiency calculation considers
- WC flush volume: Dual flush 4.0/2.6 litres is standard; single flush 6 litres is the maximum
- Basin taps: Maximum flow rate 5 l/min; aerating taps at 3-4 l/min are recommended
- Bath: Maximum capacity 170 litres to the overflow; smaller baths improve the calculation
- Shower: Maximum flow rate 8 l/min (for the 125 l/p/d target); 6 l/min for the optional 110 l/p/d target
- Kitchen sink: Maximum flow rate 6 l/min
- Washing machine: Maximum consumption 8.17 litres per kg of laundry
- Dishwasher: Maximum consumption 1.22 litres per place setting
Optional 110 l/p/d Target
Achieving the tighter target typically requires
- Lower flow shower heads (6 l/min or less)
- Smaller baths or shower-only bathrooms
- Dual flush WCs at 4.0/2.6 litres or lower
- Rainwater harvesting or greywater recycling (for the most challenging specifications)
Labelling
- Water fittings should display a Water Label (voluntary scheme) or EU Water Label showing the flow rate
- Specifiers should check flow rates against the Part G calculator to confirm compliance
Practical Compliance Tips
- Run the Part G water efficiency calculator during the design stage to confirm the specification will comply
- Specify flow-restricted shower heads; many occupants will not notice the difference between 8 l/min and 6 l/min with a well-designed aerated head
- Dual flush WCs with 4.0/2.6 litre flush volumes are widely available at no cost premium
- Provide homeowner information explaining how to use dual flush mechanisms (many people do not realise there are two buttons)
- For the 110 l/p/d target, consider whether a bath is needed in all bathrooms; a shower-only en suite significantly reduces consumption
- Rainwater harvesting for WC flushing and garden use can contribute to the calculation but adds cost and maintenance
- Keep the water efficiency calculation for Building Control sign-off