B-26 Assessment of operational water use in simplified LCA

Aspect B-26 Assessment of operational water use in simplified LCA
The operational water use assessment includes water used during the operation of the building, together with the associated environmental impacts and aspects, including the production of drinking water and wastewater treatment. A link between domestic hot water and energy use should also be considered.

related study objective

stand-alone LCA comparative assertion

related study phase

goal and scope definition inventory analysis (LCI) impact assessment (LCIA) interpretation reporting

relevant for

new buildings existing buildings construction products screening LCA simplified LCA complete LCA
Provisions Assessment of the water consumption during the use phase should be included in the LCA studies in order to be consistent within the overall assessment methodology (the use of a ‘net fresh water’ indicator for the various life cycle phases). Water consumption during the use phase is usually the most important, compared with the other phases of the life cycle.Operational water use may be assessed using a top-down approach for simplified LCA (see guidance). The upstream and downstream processes linked to the operational water use may be modelled using generic LCA data.
Rules from:

EN 15978 Boundary of the operational water use (Module B7)EN 15978 states that the boundary of operational water use should include water used during the normal operation of the building together with the associated environmental impacts due to its treatment (before and after use). This includes drinking water, water for sanitation, domestic hot water, irrigation, water for heating, cooling, ventilation and humidification, and other specific water uses (e.g. fountains, swimming pools and saunas). Water consumption of non-building-related equipment (e.g. dishwashers, washing machines) could be included within the assessment. This issue should be reported separately.

EN 15804 B6, use of energy and B7, use of water
In order to calculate the water consumption for simplified LCA, a methodology based on a top-down approach could be followed. It consists in estimating the total consumption by taking into account the economies that can be achieved by using some water saving devices (e.g. dual-flush toilet systems) compared with the average water consumption (e.g. 50 m3/year/person, i.e. 115 m3/dwelling/ year) or the extra consumption due to some specific systems (e.g. fountains, swimming pools, saunas).In addition to the volume of water consumed, the environmental impacts linked to the production, respectively wastewater treatment should also be considered.For screening and simplified LCA only the most representative technologies should be considered by using generic LCA data available in background LCI databases (e.g. ELCD, GaBi or Ecoinvent).

Additional guidance

Some of the labelling schemes (e.g. DGNB) also use a water indicator that is based on the average water consumption of the sanitary system, rainwater and greywater use. Such an indicator may be of help in calculating operational water use for simplified LCI (Module B7).

Any comparative assertion should be supported by a sensitivity analysis of the various parameters and hypotheses considered during the assessment, especially regarding user behaviour. The baseline scenario should be developed by using default values for all the parameters, defined according to statistics on the most common current values. Regular updating is therefore necessary (as the various equipment characteristics evolve relatively quickly).

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