Water Resources in Life‐Cycle Impact Assessment: Considerations in Choosing Category Indicators

Abstract

Summary Water is one of many resources, wastes, and pollutants considered in life‐cycle assessment (LCA). The widely used indicator for water resources, the total input of water used, is not adequate to assess water resources from a sustainability perspective. More detailed indicators are proposed for water resources in two areas essential to water sustainability: water quantity and water quality. The governing principles for a consideration of water quantity are that (1) the water sources or LCA inputs are renewable and sustainable and (2) the volume of water released or LCA outputs are returned to humans or ecosystems for further use downstream. The governing principle for a consideration of water quality is that the utility of the returned water is not impaired for either humans or ecosystems downstream. Water quantity indicators are defined for water use, consumption, and depletion to reveal the sustainable or nonsustainable nature of the sources. A flexible set of water quality indicators for various factors that may impair water quality are then discussed, including the LCA study choices, technical challenges, and trade‐offs involved with such indicators. Indicator selection from this set involves the underlying concern or endpoint represented by the indicator and the level and accuracy of decision‐making information that the indicator must provide. With significant differences in emissions among systems studied using LCA and different purposes of the LCA studies themselves, a single, default set of water quality indicators applicable to all systems studied with LCA is problematic. The proposed water quantity and quality indicators for LCA studies are also intended to be compatible with environmental management and reporting systems so that data needs are not duplicated and interpretation for one does not contradict or sow confusion for the other.

Assessing the Environmental Impacts of Freshwater Consumption in LCA

“…Ideally, the type of use, source of water, and geographical location should also be documented. As recognized in earlier research (4), in-stream and off-stream use need to be distinguished. Water withdrawals represent off-stream use, while in-stream use denotes the use of water in the natural water body, e.g., hydropower production and transport on waterways.…”

“…Even less attention is paid to water use in life-cycle impact assessment (LCIA), in which emissions and resource uses are grouped and compared according to their environmental impacts (e.g., global warming or resource depletion). So far, impacts on water resources have only been described qualitatively (4), with the exception of the Ecological Scarcity 2006 method (UBP06). The Ecological Scarcity method quantifies eco-factors on the basis of defined environmental targets (5) without addressing specific damages to human health and ecosystems.…”

Assessing freshwater use impacts in LCA: Part I—inventory modelling and characterisation factors for the main impact pathways

“…used for cooling or as input to desalination plants). Owens (2002) further details whether water is used in-stream (e.g. in a power dam) or is withdrawn off-stream.…”

“…− non-evaporative water use ('water use' according to Owens 2002: water is returned to the original basin and may be used by other users after leaving the system) and − evaporative water use ('water consumption' according to Owens 2002: water is dissipated and not immediately available after use). Obviously, non-evaporative water may return to a different system, which requires a proper definition of the temporal and spatial system boundaries: when and where do we consider that water leaves a system and/or becomes available to other users?…”

“…Recently, some authors have suggested ways to progress beyond merely quantifying the volume of water used per functional unit. Owens (2002) clarifies the definitions of different water inputs to (sources) and outputs from (dispositions) the system, key to a proper inventory of freshwater use, and suggests the qualitative aspects that should be factored into water assessment in LCA. Brent (2004) stresses the need for spatial differentiation, but suggests simply adding a kg of water used with no further characterisation along the life cycle stages.…”