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Wat 01 Water consumption

Number of credits available Minimum standards
5 Yes


To reduce the consumption of potable water for sanitary use in new buildings from all sources through the use of water efficient components and water recycling systems.

Assessment criteria

The following is required to demonstrate compliance for:

Up to five credits

  1. An assessment of the efficiency of the building’s domestic water-consuming components is undertaken using the BREEAM Wat 01 calculator.
  2. The water consumption (L/person/day) for the assessed building is compared against a baseline performance and BREEAM credits awarded based upon Table 35 .
  3. The efficiency of the following ‘domestic scale’ water-consuming components must be included in the assessment (where specified):
    1. WCs
    2. Urinals
    3. Taps (wash hand basins and where specified kitchen taps and waste disposal unit)
    4. Showers
    5. Baths
    6. Dishwashers (domestic and commercial sized)
    7. Washing machines (domestic and commercial or industrial sized).

The BREEAM Wat 01 calculator defines the building types and activity areas for which the above components must be assessed.

  1. Where a greywater and/or rainwater system is specified, its yield (L/person/day) is used to off-set non-potable water demand from components that would otherwise be supplied using potable water.
  2. Any greywater systems must be specified and installed in compliance with BS 8525-1:2010 Greywater Systems - Part 1 Code of Practice1BS 8525-1:2010, Greywater systems – Part 1 code of practice, BSi, 2010.. Any rainwater systems must be specified and installed in compliance with BS 8515:2009+A1:2013 Rainwater Harvesting Systems - Code of practice2BS 8515:2009+A1:2013, Rainwater harvesting systems – Code of practice, BSi, 2009..
  3. Healthcare and prison buildings: refer to the relevant compliance note for additional criteria regarding the specification of particular water-consuming component controls.

Checklists and tables

Table 35 BREEAM Credits available for percentage improvement over baseline building water consumption

% improvement No. of BREEAM credits
12.5% 1
25% 2
40% 3
50% 4
55% 5
65% Exemplary performance

Note: for some building types an alternative approach to compliance must be used to award credits (for further information please refer to the Methodology section, below, and the BREEAM Wat 01 calculator)

Compliance notes




Shell and core


Applicable assessment criteria

All criteria

Option 1 - Shell only: This issue is not applicable

Option 2 - Shell and core: This issue is applicable subject to CN1.1 below

Refer to Appendix D – BREEAM UK New Construction and Shell and Core Project Assessments for a more detailed description of the above shell and core assessment options.


Shell and core assessments

Option 2 - Shell and core

Compliance for this issue must be assessed on the basis of all water-consuming components and greywater and/or rainwater systems specified and installed by the developer. Components or systems listed in the criteria and sited within tenant areas that are not being specified by the developer, but will be specified by the tenant, do not need to be assessed for a shell and core project.


Minimum standard not met

Option 1-Shell only: the minimum standard will not be applied to shell only assessments.

Option 2 -Shell and core: where components are not being specified and installed by the developer but will be specified by the tenant, the minimum standard for this issue will not prevent the assessment from achieving a BREEAM rating.

Simple buildings


Applicable assessment criteria

All criteria relevant to the building type and function apply.



No fittings present

Where a project under assessment contains none of the specified components, the performance specification for components provided in facilities in an adjacent and accessible building must be used in the calculation, i.e. those facilities most likely to be used by the occupants and visitors of the assessed building.

This rule also applies where a project under assessment consists solely of an extension to an existing building, i.e. where the extended building contains no new sanitary facilities because there are facilities present within the existing building.

Building specific



Components in healthcare facilities

See criterion 6.

In addition to meeting the criteria defined above, the flushing control for each WC or urinal in a healthcare facility must be suitable for operation by patients with frail or infirm hands or activated by electronic sensors.

Components in clinical areas may be omitted from the calculation. For the purpose of this compliance note ‘clinical areas’ refers to all areas where a scrub-up trough, clinical sink or clinical basin is installed. This is not an exhaustive list and guidance should always be sought from the appropriate professional, such as a health authorities Infection control officer or a client infection control representative or equivalent, to ascertain areas of exemption specific to infection control and other considerations.

Although exempt, HTM07-04 contains guidance on water savings from medical-related activities. Furthermore, in some cases, the use of water efficient fittings and appliances may not be appropriate to the needs of the patient, and inappropriate specification may adversely affect the incidence and propagation of infections. In such instances, the assessor will need to confirm with BRE Global whether components from the relevant building areas are exempt. The design team should also consult NHS guidelines concerning appropriate selection of sanitary fittings and fixtures and the control of Legionella.



Components in prison cells on HM Prison developments

See criterion 6.

In addition to meeting the criteria defined above, the following requirements apply:

Where sanitary components are specified within a prison cell, a volume controller must be specified on the individual fittings or water supply to each cell. A volume controller is an automatic control device to turn off the water supply once the maximum pre-set volume is reached within a defined period.


A non-domestic building’s water efficient performance is determined using the BREEAM Wat 01 calculator in one of two ways, using either the standard approach (common building types) or alternative (other building type) approach. Each approach is summarised below.

Standard Wat01 method

The standard BREEAM method determines water efficiency (measured in L/person/day and m3/person/yr) for a building based on the buildings actual component specification and default usage patterns for the building type and its activity areas. This modelled 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 baseline component specification is equivalent to the water efficiency of industry standard components (see Table 36 ), steered by the minimum levels required by the Water Supply (Water Fittings) Regulations. The BREEAM percentage improvement benchmarks have then been determined based on progressively more efficient standards for water-consuming components and, for the higher levels of performance, the specification of greywater and rainwater systems.

The standard approach is the default method for calculating water efficiency of a BREEAM-assessed building and is that used for most of the common building types, where usage data are available. For buildings types where usage data are not available, and therefore the standard approach of determining performance cannot be used, an alternative approach to compliance must be used (described below). Refer to the BREEAM Wat 01 calculator for the current list of building types which can be assessed using the standard approach.

Alternative Wat01 method

Where it is not possible to use the standard approach to determine the buildings water consumption total (L/person/day) the assessment can be completed on an elemental basis, as follows:

  1. Using the list of applicable domestic scale water-consuming components (see criterion 3), determine those that are specified/present in the assessed building.
  2. Compare the actual specification for each component type with the table of water efficient consumption levels by component type (Table 36 ) 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.
  3. Define each component’s level of performance in the 'Other building type calculator' worksheet of the BREEAM Wat 01 calculator.
    1. For the alternative approach, the calculator applies a building type specific weighting to each component level to reflect its ‘in-use’ consumption relative to the other components present. A component with high ‘in-use’ water consumption therefore has a larger weighting than one with lower ‘in-use’ consumption and contributes relatively more to the building’s overall level of performance under this BREEAM issue.
    2. The weightings are derived from data on actual water consumption per day from non-domestic buildings, sourced from BNWAT223BNWAT22: Domestic water consumption in domestic and non-domestic properties (version 1.1). Market Transformation Programme, 2007.. They can be found in the BREEAM Wat 01 calculator.
  4. Based upon the performance categorisation of each component type and the component weighting, the calculator will determine an overall level of performance and award the relevant number of BREEAM credits as follows:
  Greywater/rainwater level achieved
Overall component level _ 4 5
Baseline 0 credits 1 credit 2 credits
Level 1 1 credit 2 credits 3 credits
Level 2 2 credits 3 credits 4 credits
Level 3 or 4 3 credits 4 credits 5 credits
Level 5 4 credits 5 credits 5 credits


  1. An innovation credit for exemplary level performance can be awarded where the component specification achieves level 5 and > 95% of WC or urinal flushing demand is met using recycled non-potable water.
  2. Due to the use of the weightings, the overall component level achieved will not necessarily be a whole number, e.g component level 4. Where this is the case the methodology will always round down to the nearest component level and therefore BREEAM credit(s) level, e.g. if the component specification achieved is 3.6 credits, the actual number of credits awarded is 3 credits (the methodology will not round up to 4 credits because the performance specification for 4 credits has not been achieved).
  3. Where the assessed building development has multiple specifications for the same water-consuming component type, the number of fittings and component level achieved for each specification can be entered in the 'Other building type calculator'. Using this information, the calculator will determine the building’s aggregated performance level for that component type.

Please note: while attempts have been made to align the benchmarking of both methodologies described above, they do determine performance in different ways. The number of BREEAM credits awarded by each method could therefore differ for the same water component specification. This could lead to variation in the credits achieved when applying BREEAM New Construction to a number of different building types that form a part of the same overall development.

Component type

Table 36 outlines the standards, by component type, used to define the performance levels set in BREEAM. These defined levels of efficiency have been steered by a range of published sources of information (see references4AECB Water Standards: Delivering buildings with excellent water and energy performance, vol 2 The water standards, technical background report (version 1), Grant, Thorton, AECB, 2009.BNWAT22: Domestic water consumption in domestic and non-domestic properties (version 1.1). Market Transformation Programme, 2007.BNWAT07: Baths - water efficiency performance tests (version 2.0). Market Transformation Programme, 2007.BNWAT23: Reliability of information on water consumption of appliances (version 1), Market Transformation Programme, 2007.BS6465-3:2006, Sanitary installations – Part 3: Code of practice for the selection, installation and maintenance of sanitary and associated appliances. BSi, 2006.CIRIA W10, Key Performance Indicators for water use in hotels, Rachel Waggett and Catherine Arotsky, CIRIA, 2006.CIRIA W11, Key Performance Indicators for water use in offices, Waggett, Arotsky, CIRIA, 2006.Conserving water in buildings, a practical guide. Environment Agency, 2007.Enhanced Capital Allowance Water Technology List criteria: by Entec UK Ltd for CLG: Research to Assess the Costs and Benefits of Improvements to the Water Efficiency of New Non-household Buildings, Final Report, Oct 2009.SD129: Certification and Listing of Low Flush WC appliances. BRE Global, 2008SD174: Certification and Listing of Water Efficient Terminal Fittings. BRE Global, 2008.SD175: Certification and Listing of Water Efficient Baths. BRE Global, 2008.The Building Regulations 2000, Part G: Sanitation, hot water safety and water efficiency (2010 edition). HM Government.Waterwise: Efficiency Calculator for New Dwellings. Communities and Local Government, 2009.Water efficient product labelling scheme: Supply (water fittings) Regulations 1999, DEFRA.Sustainable Products 2006: Policy Analysis and Projections, Market Transformation Programme, Defra, 2006.Water UK - Macerators, the impact on sewers: Efficient Buildings, water and planning, guidance for planners http://www.water and therefore reflect robust levels of typical, good, best and exemplary practice.

Table 36 Water efficient consumption levels by component type

Component Performance levels (quoted numbers are minimum performance required to achieve the level)
  Base 1 2 3 4 5 Unit
WC 6 5 4.5 4 3.75 3 Effective flush volume (litres)
Wash hand basin taps 12 9 7.50 4.50 3.75 3 litres/min
Showers 14 10 8 6 4 3.50 litres/min
Baths 200 180 160 140 120 100 litres
(2 or more urinals)
7.50 6 3 1.50 0.75 0 litres/bowl/hour
(1 urinal only)
10 8 4 2 1 0 litres/bowl/hour
rainwater system
0% 0% 0% 25% 50% 75% % of WC/urinal flushing demand met using recycled non-potable water
Kitchen tap:
12 10 7.50 5 5 5 litres/min
Kitchen taps:
restaurant (pre-rinse nozzles only)
10.30 9 8.30 7.30 6.30 6 litres/min
Domestic sized dishwashers 17 13 13 12 11 10 litres/cycle
Domestic sized washing machines 90 60 50 40 35 30 litres/use
Waste disposal unit 17 17 0 0 0 0 litres/min
Commercial sized dishwashers 8 7 6 5 4 3 litres/rack
Industrial sized washing machines
14 12 10 7.50 5 4.50 litres/kg

Please note that specifying components for a building in accordance with the above levels will result, in most cases, in the corresponding number of BREEAM credits being achieved. However, please bear in mind that the component specifications above are akin to thresholds between each level. Therefore caution should be taken when defining a component specification for a BREEAM-assessed building using exactly the same levels as the threshold levels. It is recommended that, where Wat 01 BREEAM credits are being targeted, the performance of a particular building’s component specification is verified using the BREEAM Wat 01 calculator before committing to a particular specification and ordering/installing components. This will provide greater assurance that the component specification achieves the targeted number of BREEAM credits.

Water-consuming components - data requirements

Table 37 defines for each component type the appropriate data that will need to be collected from manufacturers’ product information to complete the assessment

Domestic component Data requirements


Actual maximum or, where dual flush, effective flush volume in litres/use.
Urinals Flush volume in litres/use for single use flush urinals. For cistern fed systems, the flushing frequency/hour and cistern capacity in litres.

Flow rate of each tap, at full flow rate in litres per minute measured at a dynamic pressure:

For high pressure (Type 1) taps - 3 ± 0.2 bar (0.3 ± 0.02 MPa) OR

For low pressure (Type 2) taps - 0.1 ± 0.02 bar (0.01 ± 0.002 MPa)

(BS EN 200:2008, sanitary tapware, single taps and combination taps for supply systems of type 1 and 2. General technical specifications)

This includes any reductions achieved with flow restrictions.


Flow rate of each shower at the outlet using cold water (T 30˚C), in litres per minute measured at a dynamic pressure

3 ± 0.2 bar (0.3 ± 0.02 MPa) for high pressure (Type 1) supply systems


0.1 ± 0.05 bar (0.01 ± 0.005 MPa) for low pressure (Type 2) supply systems

(BS EN 1112:2008, Sanitary tapware. Shower outlets for sanitary tapware for water supply systems type 1 and 2. General technical specifications).

Kitchen taps Maximum flow rate litres/minute.

Capacity to overflow in litres. Taps on baths should not be included in the calculation, as the water consumption from bath taps is taken account of in the use factor for baths. The calculation of water consumption for baths will assume 40% of the capacity to the overflow. This is to reflect that:

  1. Users tend not to fill the bath to overflow; and
  2. The displacement effect the user has on the actual volume of water required for a bath.
Dishwasher Litres/cycle for domestic applications and/or appliances or litres/rack for commercial applications and/or appliances.
Washing machine Litres/use for domestic applications (for a typical wash cycle) and/or appliances or litres/kg for commercial applications and/or appliances, e.g. in hotels.
Waste disposal unit Flow rate in litres/minute.

Unspecified water-consuming components

As the methodology and BREEAM credits for water efficiency compare the buildings modelled water consumption performance against the performance of a baseline specification for the same component types, where a component type is not specified it is not accounted for in the methodology, i.e. the component is excluded from both the proposed and baseline building. Therefore no benefit is gained in terms of BREEAM performance, by deciding not to specify a particular component. However, the methodology will reflect the reduction in overall water consumption (litres/person/day) for the building, as a result of not specifying a particular component.

Buildings with a greywater and rainwater system(s)

The following information is required where a greywater and/or rainwater system is specified:

Rainwater: In accordance with BS 8515 ‘intermediate approach’:

  1. Collection area (m²)
  2. Yield co-efficient (%)
  3. Hydraulic filter efficiency (%)
  4. Rainfall (average mm/year).

Rainwater: In accordance with BS 8515 ‘detailed approach’:

  1. Daily rainfall collection (litres)

Greywater: in accordance with BS 8525 :

  1. Manufacturer or system designer details.
  2. The percentage volume of waste water collected (and reused) from the following (where relevant); wash hand basins, showers, kitchen basins, dishwashers, baths, washing machines and sources of waste water from non-domestic components.

Where greywater and/or rainwater systems are specified, a minimum level of component efficiency must be achieved to award 4 or 5 BREEAM credits and the exemplary level credit. This is to avoid awarding a higher number of BREEAM credits where performance from less efficient fittings is off-set by the specification of a greywater and/or rainwater collection system.

The intention behind this is to ensure demand reduction is prioritised before offsetting consumption. Where a greywater/rainwater system is specified/installed, the component specification must achieve a percentage reduction in water consumption (over the baseline specification) equivalent to that required for 2 credits, i.e. a 25% improvement. Where this level is achieved, all of the total water demand met by greywater/rainwater sources can contribute to the overall percentage improvement required to achieve BREEAM credits. If it is not achieved, the percentage of greywater/rainwater allowable will be equivalent to the percentage improvement in water consumption achieved for the component specification, i.e. percentage improvement on baseline performance.

For example, if a 20% improvement only is achieved, and therefore the building is not meeting the 25% requirement, only 20% of the water demand met via greywater/rainwater sources can be used to off-set water consumption from the micro components. This minimum requirement does not apply where only 1, 2 or 3 credits are sought or where no greywater/rainwater system is specified, i.e. percentage improvement is based solely on the water efficiency of the micro-component specification.

BRE Global may allow some exemptions to this rule in instances where a particular fitting type requires a high flow rate due to specialised end user requirements, and its specification prevents compliance with 25% improvement.

Buildings with a mixture of different functional areas

For the majority of buildings using the standard Wat 01 method, the BREEAM Wat 01 calculator defines the building type and range of different water-consuming activity areas within that building; for example, a retail development with sales area and goods storage or an office that includes a canteen and gym. However, where carrying out a single assessment of a building/development which consists of a diverse mix of activity areas/building types, all of which can be assessed separately within the calculator, the following applies:

Determine the building’s total water consumption performance by carrying out separate assessments for each relevant activity area/building type. On completion of each assessment, the assessor will need to determine the percentage improvement as follows:

overal improvement in percentage equals hundred times one minus a fraction between THE sum from one to n of the modelled net water consumption times the total default occupancy rate AND THE sum from one to n of the modelled baseline water consumption times the total default occupancy rate


I = Overall improvement (%)
TnAct = the modelled net water consumption (L/person/day) for each building type
TnBase = the modelled baseline water consumption for the corresponding building type
TnOcc = the total default occupancy rate for the corresponding building type.

Where greywater/rainwater systems are specified, the assessor should take care to avoid unintended double counting of the yield from such systems and using it to off-set demand for each activity area/building type.

Fixed water use

The BREEAM water efficiency calculation includes an allowance for fixed water use. This includes water consumption for vessel filling (for building users drinking water), cleaning in kitchens and food preparation in buildings with a catering facility. Fixed uses are included to provide greater accuracy in reporting of the building’s overall estimated water consumption. As these uses are fixed for both actual and baseline building models, their totals do not influence the achievement of BREEAM credits.

Other permissible component demand for non-potable water

The focus of this BREEAM issue is the performance of the building's permanent domestic scale water-consuming components. Where a grey water or rainwater system is specified, the yield from the system should be prioritised for such uses, i.e. WC or urinal flushing. However, where the building demonstrates that it has other consistent (i.e. daily) and equivalent levels of non-potable water demand, and such demands are intrinsic to the building’s operation, then it is permissible for the demand from these non-domestic uses to be counted, i.e. the demand for rainwater/greywater yield from such systems/components can be used as well as, or instead of non-potable water demand from the building's WC/urinal components. Examples of consistent and intrinsic demands could include laundry use in hotels/multi-residential developments or horticultural uses in garden centres, botanical gardens and golf courses. Demand for general landscaping and ornamental planting irrigation are not considered as equivalent/intrinsic by BREEAM.

Other permissible sources of non-potable water

The methodology allows for the collection and recycling of non-potable water from the relevant components listed in the criteria i.e. taps, showers, baths and dishwashers or washing machines. In addition, where non-potable water is collected from a non domestic component or source that is intrinsic to the building, then the amount collected can be accounted for in the methodology. This could include for example wastewater from active hygiene flushing, i.e. a regular hygiene flushing programme to minimise poor water quality in a potable cold or hot water system. In order for the method to account for this total, the design team will need to confirm to the assessor the yield from the component/system (in litres) and the frequency of that yield (in days), i.e. if once a week, the frequency would be seven days.


Criteria Interim design stage
Final post construction stage

One or more of the appropriate evidence types listed in The BREEAM evidential requirements section can be used to demonstrate compliance with these criteria.

1 A completed copy of the BREEAM Wat 01 calculator As per interim design stage
1 Documentary evidence supporting the data used to complete the Calculator tool. As per interim design stage

Additional information

Relevant definitions

BREEAM Wat 01 calculator for New Non-Domestic Buildings
The BREEAM Wat 01 calculator is a method for the assessment of water efficiency in most common types of new non-domestic buildings. The calculator assesses the contribution that each internal domestic scale water-consuming component (as listed in the criteria) has on whole building water consumption. The calculator and accompanying guidance on its application is available separately from this Scheme Document.
Please note; the calculator is a compliance tool and not a design tool for water demand and drainage systems. The tool uses default usage and occupancy rates to provide a benchmark of the typical consumption given the specified fittings (in L/person/day and m3/person/year) and their impact on the building's overall water efficiency. Due to the impacts and differences of actual user behaviour and occupancy rates the results of the method will not reflect directly the actual water use during building operation. The results from the methodology should, therefore, not be used for the purpose of comparison with or prediction of actual water consumption from a non-domestic building.
Domestic scale components
Domestic scale components include water consumed (potable and non-potable) by internal building components including kitchen taps, wash hand basin taps, baths, showers and dishwashers, WCs, urinals, washing machines and waste disposal units.
Effective flush volume
The effective flush volume of a single flush WC is the volume of water used for one flush.
The effective flush volume of a dual flush WC is the ratio of full flush to reduced flush. This is taken to be one full flush for every three reduced flushes for non-domestic buildings and one full flush for every two reduced flushes in domestic (residential) buildings/areas. The effective flush volume can therefore be calculated as follows, using a 6/4 litre dual flush volume WC as an example:

The differing ratio between non-domestic and domestic buildings reflects the different patterns of user behaviour between these building types.
Greywater recycling
The appropriate collection, treatment and storage of domestic wastewater (which is defined as that discharged from kitchens, baths or showers, laundry rooms and similar) to meet a non-potable water demand in the building e.g. WC flushing, or other permissible non-potable use on the site of the assessed building.
Potable water
Water suitable for human consumption that meets the requirements of Section 67 (Standards of Wholesomeness) of the Water Industry Act 19915Great Britain, The Water Industry Act 1991. London: The Stationery Office is referred to as 'wholesome water'.
Non-potable water
Any water other than potable water, also referred to as unwholesome water (BS 8525, see references).
Rainwater recycling
The appropriate collection and storage of rainwater run-off from hard outdoor surfaces to meet a non-potable water demand in the building e.g. WC flushing, or other permissible non-potable use on the site of the assessed building.
Clinical areas
Refer to BREEAM issue Hea 01 Visual comfort.

Other Information


BREEAM UK New Construction non-domestic buildings technical manual 2014
Reference: SD5076 – Issue: 5.0
Date: 23/08/2016
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