Part G Water Calculations

Water calculations and the Code for Sustainable Homes or Building Regulations.

The requirement of your Water Calculation will vary depending on what level of CfSH you are working to, of course we can help with a fast, trouble free tailored calculation to ensure a successful result regardless if the calculation is for a New Build, Conversion or Refurb. Most Building Control, private or public, will require a water calculation if you intend on installing larger than usual bathroom systems. Some will require them as standard.

Why Do You Need Part G Water Calculations?

Building regulations require that developments meet the minimum 125 litre per-person-per-day limit, this was set in the Part G Building Regulations.

If the development is to meet any level of the Code for Sustainable Homes, you will require a reduction of ‘potable water use’ further through the Wat 1 category.
Each Code level hass a hard limit on the amount of Litres that can be consumed daily – this is shown via a calculation, which is determined by occupancy, fittings and flow rates.


The limits are set as follows:

Level 1 & 2 – Less than or equal 120 L/P/day
Levels 3 & 4 – Less than or equal 105L/P/day
Levels 5 & 6 – Less than or equal 80L/P/day
Credits are available for meeting requirements.

WM Diagnostics
staff will assist you in meeting these requirements and are able to give advice on the methodology of doing so.

The Water Efficiency Calculator for New Dwellings

Our Part G water calculations are carried out using the Governments national calculation methodology.

This calculation will provide everything required in a clear, concise manner for yourself and Building Control.

Need help with Part G Water Calculations?

WM Diagnostics Staff are able to give advice and even carry out calculations over the phone, just give us a call on 01822 833227 or Contact Us