The issue of considering water quality in life cycle assessment of water use

Available water-use impact assessment methods provide insight into the potential impacts of water use. As water-use impact assessment models develop, the amount of inventory information required increases. Among the parameters needed, water quality is identified as essential since water quality can also influence availability to meet specific water users’ needs. It was argued that these users could be deprived and suffer consequences. However, data on water quality may be difficult to gather and the related impact pathways may entail risks of double counting with emission characterization models. This paper answers to which extent water quality must be considered in water-use impact assessment.

The role and the necessity of water quality information are discussed along the cause-effect chain of three water-use interventions: water consumption (WU1), water degradation (WU2), and water quality improvement (WU3). Each intervention is individually explored and put in perspective with the human health, ecosystem quality, and natural resources areas of protection (AoPs).

Our findings suggest that, for WU1, the quality of input water elementary flow might be useful to know the pressure on the resource and the affected users, but alternative methods that avoid the need for this scarce information can be built. WU1 (including quality information) and WU2 are currently assessed by linking water users to water functionality via water quality, which may be misleading in areas unable to compensate for lacking water of a certain quality. In these areas, low-quality water may still be consumed even if it does not fulfill a quality standard. Thus, WU2 would rather lead to toxic impacts instead of to water deprivation impacts since this latter pathway assumes that polluted water below the quality standard will no longer be used. Hence, water deprivation impacts should only focus on WU1 to avoid double counting with emission characterization models. For WU3, no LCA approach exists to meaningfully quantify its environmental benefits, but an indicator for water as a natural resource may be a solution.

This study improves the understanding of the role of water quality information in water-use impact assessment and brings more consistency between existing (and future) models. Further research is required to better understand the positive effects induced by water quality improvement and the effects on freshwater resources themselves. More generally, a framework is required to identify how freshwater resources can be defined as an entity to protect within the AoP natural resource.