As freshwater is a vital yet often scarce resource, the life cycle assessment community has put great efforts in method development to properly address water use. The International Organization for Standardization has recently even launched a project aiming at creating an international standard for ‘water footprinting’. This paper provides an overview of a broad range of methods developed to enable accounting and impact assessment of water use. The critical review revealed that methodological scopes differ regarding types of water use accounted for, inclusion of local water scarcity, as well as differentiation between watercourses and quality aspects. As the application of the most advanced methods requires high resolution inventory data, the trade-off between ‘precision’ and ‘applicability’ needs to be addressed in future studies and in the new international standard.

Purpose: Assessing impacts of abiotic resource use has been a topic of persistent debate among life cycle impact assessment (LCIA) method developers and a source of confusion for life cycle assessment (LCA) practitioners considering the different interpretations of the safeguard subject for mineral resources and the resulting variety of LCIA methods to choose from. Based on the review and assessment of 27 existing LCIA methods, accomplished in the first part of this paper series (Sonderegger et al. 2020), this paper provides recommendations regarding the application-dependent use of existing methods and areas for future method development. Method: Within the “global guidance for LCIA indicators and methods” project of the Life Cycle Initiative hosted by UN Environment, 62 members of the “task force mineral resources” representing different stakeholders discussed the strengths and limitations of existing LCIA methods and developed initial conclusions. These were used by a subgroup of eight members at the Pellston Workshop® held in Valencia, Spain, to derive recommendations on the application-dependent use and future development of impact assessment methods. Results and discussion: First, the safeguard subject for mineral resources within the area of protection (AoP) natural resources was defined. Subsequently, seven key questions regarding the consequences of mineral resource use were formulated, grouped into “inside-out” related questions (i.e., current resource use leading to changes in opportunities for future users to use resources) and “outside-in” related questions (i.e., potential restrictions of resource availability for current resource users). Existing LCIA methods were assigned to these questions, and seven methods (ADP_{ultimate reserves}, SOP_URR, LIME2_endpoint, CEENE, ADP_{economic reserves}, ESSENZ, and GeoPolRisk) are recommended for use in current LCA studies at different levels of recommendation. All 27 identified LCIA methods were tested on an LCA case study of an electric vehicle, and yielded divergent results due to their modeling of impact mechanisms that address different questions related to mineral resource use. Besides method-specific recommendations, we recommend that all methods increase the number of minerals covered, regularly update their characterization factors, and consider the inclusion of secondary resources and anthropogenic stocks. Furthermore, the concept of dissipative resource use should be defined and integrated in future method developments. Conclusion: In an international consensus-finding process, the current challenges of assessing impacts of resource use in LCA have been addressed by defining the safeguard subject for mineral resources, formulating key questions related to this safeguard subject, recommending existing LCIA methods in relation to these questions, and highlighting areas for future method development.

The water footprint has developed into a widely-used concept to examine water use and resulting local impacts caused during agricultural and industrial production. Building on recent advancements in the water footprint concept, it can be an effective steering instrument to support, inter alia, achieving sustainable development goals (SDGs) - SDG 6 in particular. Within the research program “Water as a Global Resource” (GRoW), an initiative of the Federal Ministry for Education and Research, a number of research projects currently apply and enhance the water footprint concept in order to identify areas where water is being used inefficiently and implement practical optimization measures (see imprint for more information). With this paper, we aim to raise awareness on the potential of the water footprint concept to inform decision-making in the public and private sectors towards improved water management and achieving the SDGs.