Water Efficiency Calculations

What are Water Efficiency Calculations?photo of a running tap

In March 2015 Building Regulations Part G were amended and introduced a variety of changes, some of which affect the calculation process.  These calculations must be carried out on all new build and conversion dwellings in accordance with water performance targets in the Building Regulations Part G. This states that water consumption shall be no greater than 125 litres/person/day. Properties should be calculated in accordance with the ‘Water Efficiency Calculator for New Dwellings’ and this can be accessed using the link provided here: (http://www.planningportal.gov.uk/uploads/br/water_efficiency_calculator.pdf).

Fittings approach vs. Measured Approach.

One of the new features of the amended Building Regulations Part G is the introduction of the ‘fittings approach’. The fittings approach provides an alternative to calculating the water consumption of a given property. However, if the fittings approach is used then it is important that items installed not exceed the measurements found in Table 2.1.

part G

In addition, further optional requirements maybe imposed on a property by planning authorities if they wish to further reduce water consumption. This can be found in Table 2.2.

Problems with fittings approach

The fittings approach has been introduced to make the Water Efficiency Calculations process simpler, but this will ultimately reduce the variation and choice of items used in dwellings, which is understandably an inconvenience for some people.

Help and Guidance

Examples of some previous guidance we have provided for our clients include such items as:

  • Flow Restrictors,
  • Rainwater and Grey-Water options.

(These can greatly benefit desired targets).

Other components can also be incorporated into water calculations for you, such as:

  • Waste Disposal, and
  • Water Softeners,

(However, these will have a negative impact on the final result unless changes are made elsewhere).

High or Low Pressure System?

The Water Efficiency Calculator for New Dwellings states that flow rates (measured in litres/minute) must be taken at:

  • a dynamic pressure of 3±0.2 bar for high pressure or
  • at a dynamic pressure of 0.1±0.02 bar for low pressure systems.

(This will ultimately affect the flow rates achieved).

How to find out if I have a High or Low Pressure System?

The simplest way of finding out whether your water system is low pressure is by identifying if there is a cold water tank present in the property. This means you have a gravity fed system, which is typical of a low pressure water system. Other water systems that include combination boilers or unvented systems are typical of high pressure systems.

Please get in touch for more information or if you have any queries regarding the water efficiency calculation process.