Part G: Water Efficiency – Everything you need to know!

  • Home
  • >>
  • Blog
  • >>
  • Part G: Water Efficiency – Everything you need to know!

What is a Water Efficiency Calculation?

A water efficiency calculation is a legal requirement set out in Part G of the building regulations. These calculations are required for all new build dwellings, as well as conversions. 

Part G requires that a dwelling must not use more than 125 litres per person per day. However, some planning authorities may enforce stricter targets, such as 110 litres per person per day. Stricter targets are often implemented by London planning authorities where compliance with the London Plan is required.  If you are unsure of your target, we will check this for you.

Water calculations take the efficiency of the following into account:

  • Toilets
  • Baths
  • Showers
  • Taps
  • Dishwashers
  • Washing machines

What impacts the water calculation?

The results of a water calculation are impacted by flow rates of taps and showers, capacity of baths, toilet flushes and if rain harvesting technology or water softeners are installed.

The following table shows the maximum fittings consumption set out in Part G to achieve a target of 125 litres per person per day.

When shall I get a water calculation?

The ideal time to carry out a water calculation is at design stage. This allows us to advise on how to achieve your target and gives you time to purchase the applicable components.

Getting your water calculation completed early in the build also means that building control sign off is quicker.

What information does UKBC require to carry out a Water Efficiency Calculation?

To carry out a Water Efficiency Calculation we require a complete set of floor plans indicating the number of ‘wet rooms’ which includes the kitchen, utilities, and bathrooms. The plans should also show the number of facilities which use water such as showers, baths, sinks, toilets, dishwashers, and washing machines. This information will allow us to calculate the water consumption levels of the dwelling. 

If you have specific products that you wish to install, we need to know their flow rate/capacity to ensure that these meet your target.

How long does a Water Efficiency Calculation take?

We aim to complete most within 24 hours of instruction. Once complete, you will receive a formal report which demonstrates compliance. If compliance is not met, we will advise you on how to decrease your water consumption.

See some of our recent Water Efficiency Calculation projects below:

Related Articles


The Essential Guide to UK Building Regulations Compliance


What is a U-value?