Part G Water Calculations

The Part G Water Consumption Target is a requirement under Approved Document G of the Building Regulations that aims to reduce water usage in new homes by promoting the installation of water-efficient sanitaryware and appliances.

For most new dwellings in England, the maximum permitted water consumption is:

• 125 litres per person per day (L/person/day) – the standard Building Regulations requirement.
• 110 litres per person per day – the optional, more stringent target that may be required by the local planning authority in areas of water stress or where local planning policies apply.

To demonstrate compliance, a Part G Water Efficiency Calculation must be completed. This calculation assesses the predicted water consumption of the property based on the specification of fixtures and fittings, including:

• Toilets
• Showers
• Baths
• Wash basins
• Kitchen sinks
• Taps
• Dishwashers
• Washing machines

If the calculated water consumption exceeds the required target, changes to the specification may be needed before Building Control approval can be granted.

Many local authorities, particularly in areas of higher water demand such as parts of London and the South East, require new developments to achieve the 110 litres per person per day standard through planning conditions.

To complete a Part G Water Efficiency Calculation, we need details of the water-using fixtures and fittings that will be installed in the property. This allows us to calculate the predicted water consumption and confirm whether the dwelling complies with the requirements of Approved Document G of the Building Regulations.

Typically, we require:

• Architectural floor plans for the property.
• A sanitaryware schedule or specification, if available.
• The manufacturer and model number of all water-using fixtures and fittings.
• Flow rates or water consumption data for:
  • Toilets
  • Wash basins
  • Kitchen sinks
  • Bath taps
  • Showers
  • Baths
• Details of any:
  • Washing machines
  • Dishwashers
  • Rainwater harvesting systems
  • Greywater recycling systems
• Confirmation of whether the property needs to achieve the standard 125 litres per person per day target or the optional 110 litres per person per day target required by the local planning authority.

Don’t worry if you don’t have all of this information available. We regularly work with architects, developers, builders and homeowners during the design stage and can advise on suitable water-efficient products that will help your development achieve compliance.

Most reports can be completed within a few working days once the required information has been received.

In most cases, yes. A Part G Water Efficiency Calculation is required for new-build homes in England to demonstrate compliance with Approved Document G of the Building Regulations.

The calculation confirms that the property’s predicted water consumption does not exceed the maximum permitted target of:

• 125 litres per person per day – the standard requirement under the Building Regulations.
• 110 litres per person per day – where a local planning authority has adopted the optional, more stringent water efficiency standard.

A Part G Water Calculation is commonly required for:

• New-build houses.
• New-build flats and apartments.
• Self-build and custom-build homes.
• Residential developments of any size.
• Some property conversions or change-of-use projects where Building Regulations require compliance with Part G.

Your Building Control Body or local planning authority will usually request the completed Part G Water Efficiency Calculation before issuing final approval.

Yes. Our reports are suitable for Building Control approval and can be issued alongside SAP calculations where required.