New Construction / UK / 2011 / 05 - Water /

Wat 01 - Water Consumption

Information correct as of 5thDecember 2020. Please see for the latest compliance information.

Alternative calculation method - KBCN0547

Where it is not possible to use the standard approach to determine the building’s total water consumption, the assessment can be completed on an elemental basis. This applies even in cases where the Wat 01 Excel calculator tool has a section for a broader building type, but the defined activity areas do not match the specific project under assessment. For example, although Wat 01 calculator includes a retail calculator, bars and restaurants should be assessed using the alternative calculation method, as no relevant data is available for the specific activity within retail. Where the activity areas of the building under assessment do not allow using the relevant building type’s calculator, then the alternative calculation approach should be used.

Alternative method performance levels and credits - KBCN1007

Specifying water component performance levels according to the levels of the alternative calculation method does not equate directly to the number of credits achieved. For example, choosing all components with a level 3 performance will not equate to the achievement of 3 credits.

Commercial dishwasher appropriate data - KBCN0687

If the component is present in the building but the appropriate data is unavailable from the manufacturer's product information i.e. uses a different unit of measurement, then the baseline performance level for the specified component should be used in the WAT 01 calculator. BRE Global is unable to provide a calculation method to convert data in to the correct unit for the WAT 01 calculator tool.

Flow rate for ‘click’ taps - KBCN0543

The flow rate for click taps should be taken as the maximum flow rate, as quoted by the manufacturer, of the lower range before the water break or 'click'. All water consumption is based on 'typical' use patterns and it is assumed that most operations of 'click' taps will be at the lower level.

Flow rate for a mixture of taps - KBCN0173

Whichever is the higher of the 'average flow rate' or the 'proportionate flow rate' should be used within the Wat 01 Calculator.  

Flow restrictors - KBCN0976

If a flow restrictor can be demonstrated to effectively reduce the flow of water and it is integral to the fitting or supply pipework (ie not easily removed by the building occupant), this can be accounted for in calculations for this Issue. Such devices must be fit-for-purpose. Proprietary flow restrictors, therefore partly-closed isolation valves, for example, are not an acceptable solution.

Flushing control – patients with frail or infirm hands - KBCN0414

When determining whether the WC fittings in healthcare facilities are suitable 'for operation by patients with frail or infirm hands', the assessor should be satisfied that this requirement has been met, as it will be product type dependent. If unclear to the assessor, evidence obtained from the relevant manufacturer confirming that their product is specifically designed, and has been tested and approved, for this purpose would be acceptable.
16/04/2018 Rewritten for clarity

Measuring the flow rate of taps - KBCN0641

On site flow rate testing can be carried out by an appropriate professional to determine the flow rate of taps. This must be overseen by the client’s facilities manager and as-built drawings must be provided to confirm the presence and location of the fitting and any flow restrictors. Note that the conditions under which the testing is completed must be recorded, i.e. the pressure and the temperature of the water. The assessor could conduct the test provided they are able to carry it out accurately.

Other buildings specified fittings worse than baseline - KBCN00021

Where the performance of a sanitary fitting is worse than the baseline level, the baseline level as specified in the manual should be input as the level of performance in the Other Buildings calculator tab of the Wat 01 tool.  

Process water to offset potable water demand - KBCN0586

Process water resulting from the building under assessment, can be considered for off-setting potable water demand from components that would otherwise be supplied using potable water, when in line with the criteria requirements for greywater systems. Process water resulting from the building under assessment can be considered as a form of greywater for the purposes of off-setting potable water demand.

Rainwater harvesting standard – BS 8515:2009 replacement - KBCN1179

BS 8515:2009 (+A1:2013 where relevant) has been withdrawn and replaced by BS EN 16941-1:2018, which can be used for new assessments. The basic approach in BS EN 16941 is equivalent to the intermediate approach in BS 8515 is. The detailed approach is still described in the same way.
The relevant schemes will be updated in the next re-issues.

Specialist assisted baths in care homes - KBCN0228

Specialist assisted baths in care homes or similar specialist applications can be excluded from the assessment of this issue. Due to the specific access and care needs of users, it may not be possible to reduce the volume of specialist assisted baths.  

Urinals – calculation of litres/bowl/hour - KBCN1010

A flushing frequency of two flushes per hour is used in the Wat 01 tool and should be applied when calculating the volume of water dispensed by urinals and compared against the water efficient consumption levels by component type for the Wat 01 issue. This method should be applied to calculate litres/bowl/hour. For example, a 13.5 L cistern feeding 3 bowls which is flushed 2 times per hour: (13.5 L / 3 bowls) x 2 times an hour = 9 litres/bowl/h.  

Using borehole water to offset water consumption - KBCN00094

Borehole water is included within our definition of "potable water" and cannot therefore be used to offset water consumption in the same way as rain or grey water harvesting. A significant amount of water used for public consumption is already drawn from aquifers and often private boreholes draw from the same aquifer that water companies use.   

Washer dryers - KBCN0699

Where a washer dryer is specified, the water consumption figure for the wash and dry cycle should be used. The drying cycle of a washer dryer is taken into account because it usually uses water during this drying process (e.g. for cooling during the drying cycle) and in some cases, this water usage can be significant.

Water consumption calculation for push and automatic shut-off taps - KBCN00052

The water consumption of push and automatic shut-off taps can be calculated for input into the Wat 01 calculator using the following steps: Step 1: Calculate the water consumption per person per use. If a tap runs for less than 20 seconds per activation, assume it will be activated twice per person for the timed duration. For example, for a tap with a flow rate of 9 litres/min and a 15 second usage duration, the water consumed per person would be: 9 x 15/60 x 2 = 4.5 litres/min. If a tap runs for 20 seconds or more per activation, assume one activation per person for the timed duration. For example, for a tap with a flow rate of 9 litres/min and a 20 second usage duration, the water consumed per person would be: 9 x 20/60 x 1 = 3 litres/min. Step 2: Multiply the water consumption figure per person by 1.5 and enter this figure into the calculator tool. Multiplying by 1.5 adjusts the consumption figure to compensate for the typical non times tap use of 40 seconds that has already been taken into account in the tool. Taking the first example above, if we multiply 4.5 litres/min by 1.5 we get 6.75 litres/min. When this is used in the tool as the flow rate specification, the consumption is 4.57 litres/person/day which more closely reflects the true level of water consumption for the push tap.  

Water consumption calculation for sensor taps - KBCN0180

The water flow rate of sensor taps can be entered directly into the flow rate cells of the Wat 01 tool. The amount of water dispensed by sensor taps for each use is determined by occupant demand in the same way as normal taps. Therefore, the default frequency of use will be applied in the Wat 01 tool and no adjustment calculation is needed for sensor taps.

Water fittings specification evidence at design stage - KBCN0420

For a design stage assessment, it is acceptable to provide data based on reasonable assumptions if the final specification of fittings is not yet available.

Water fittings used for a process related function - KBCN0418

Water fittings used for a process related function, e.g. low level ablution taps, laboratory / classroom taps, scrub-up taps, cleaners' sinks etc., should be excluded from the assessment of regulated water consumption. Only kitchen taps and those used for general hygiene washing are to be included in the assessment of regulated water consumption.
04/08/17 Added low level ablution taps (typically used for religious purposes) to exemptions.

Information correct as of 5thDecember 2020. Please see for the latest compliance information.