Last edited 18 Nov 2020

Main author

Sarah Peterson Engineer Website

BREEAM Water consumption


[edit] Aim and benefits

To reduce potable water demand through the installation of energy efficient sanitary fittings, rainwater collection and water recycling systems. Up to 5 credits are available plus an additional credit for exemplary performance.

[edit] When to consider

Design Stage RIBA Stages 3-4.

[edit] Step-by-step guidance

Credit Wat 1 is an assessment of the efficiency of the buildings water consumption compared to a baseline performance standard.

Using the BREEAM Wat 1 Calculator Tool the water consumption (litres per person per day) is assessed to suit the building type and credits awarded accordingly.

The following components are included in the assessment and must be included within the calculation where specified in the project:

If any rainwater or greywater recycling systems are proposed details must also be included.

There are two methods to assess the credit:

  1. Standard Method
  2. Alternative Method

[edit] Standard method

The standard approach is the default method for calculation.

It uses the buildings actual component specification and default usage patterns for the building type and its activity areas. The output is compared with the same output for a baseline component specification and the percentage improvement used to determine the number of BREEAM credits achieved.

The standard building types are:

[edit] Alternative method

If the development does not meet the standard building types the alternative method can be used.

Using the other buildings tab the performance level of each applicable component is assessed. This compares the actual specification for each component type with the table of water efficient consumption levels by component type (Table 36 within the BREEAM manual) to determine the level of performance for each type.

Note that the volumes quoted are maximums for that level and the % WC or urinal flushing demand is a minimum for that level.

[edit] Average flow rate calculator

The Wat 1 Calculator tool has a tab to calculate the average flow if there are various specification types and flow rates for each component type across a development.

[edit] Effective flush volume

For WC's this is calculated as follows:

The effective flush volume can therefore be calculated as follows, using a 6/4 litre dual flush volume WC as an example:

  • Non-domestic:{(6 litre x 1)+(4 litre x 3)}/4 =4.5 litre effective flushing volume.

[edit] Questions to ask while seeking compliance

[edit] Tools and resources

[edit] Tips and best practice

This BREEAM issue has minimum standards and at least 1 credit must be scored for this issue for Good, Very Good or an Excellent rating. 2 Credits must be achieved for an Outstanding rating.

Due to the minimum standards, this BREEAM issue should be reviewed as soon as possible to ensure the final BREEAM rating can be achieved.

Depending on project procurement the design team may not select the sanitary ware and fittings. In this case it is recommended that the target flow rates and flush rates in order to achieve the required credits are detailed within a performance specification or contractors prelims document to ensure that they are met.

Manufacturers information is generally the best location to find the required flow rates and flush volumes. The design team should provide this information to allow the calculator tool to be completed.

At pre-assessment and early design stage the specification of the sanitary ware may not be complete, an estimation of the likely credits that can be achieved can be calculated with the following tables found within the BREEAM Manual, however a full calculation using the calculator tool should be carried out as soon as the information is available to verify the amount of credits that can be achieved.


[edit] Typical evidence

[edit] Design stage

[edit] Post construction stage

[edit] Rainwater and greywater

The requirements are:

Rainwater: In accordance with BS8515 ‘intermediate approach’:

Rainwater: In accordance with BS8515 ‘detailed approach’:

Greywater: in accordance with BS8525 :

[edit] Applicable schemes

The guidelines collated in this ISD aim to support sustainable best practice in the topic described. This issue may apply in multiple BREEAM schemes covering different stages in the life of a building, different building types and different year versions. Some content may be generic but scheme nuances should also be taken into account. Refer to the comments below and related articles to this one to understand these nuances. See this document for further guidelines.

BRE Global does not endorse any of the content posted and use of the content will not guarantee the meeting of certification criteria.

--Sarah Peterson 15:25, 20 Feb 2018 (BST)

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