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The WULCA group, active since 2007 on Water Use in LCA, commenced the development of consensus-based indicators in January 2014. This activity is planned to last 2 years and covers human health, ecosystem quality, and a stress-based indicator. This latter encompasses potential deprivation of both ecosystem and human, hence aiming to represent potential impacts more comprehensively than any other available LCA-oriented method assessing the "water scarcity footprint" (ISO 2014).

A series of three expert workshops, including non-LCA experts from hydrology, eco-hydrology, and water supply science, was organized specifically on the topic of this generic midpoint indicator. They were held in Zurich on 10th September, in San Francisco on 5th October and in Tsukuba on 27th October 2014. In total 49 experts attended. The specific objectives of the workshops were twofold. First, it was to present the identified options of the stress-based indicator narrowed down by the active members of WULCA during the first 8 months of the project and to receive comments on the relevance, usefulness, acceptability, and focus of the selected indicator. Second, the workshop covered different challenges in the modeling of the indicator and presented the experts with background information and specific questions. This paper summarizes the discussions and outcome of these workshops. Where no agreement was reached, the working group of active members is considering all inputs received and continues the work.

The discussion covered first the question to be answered by such indicator, resulting on an agreement on the evaluation of the potential to deprive other users of water, independently of who the user is (i.e., human or ecosystems). Special attention was given to the special case of arid areas as well as the definition of environmental water requirements. Specific modeling challenges were then addressed: definition and quantification of human and ecosystem water demand, consideration of green water and terrestrial ecosystems, sources of data, distinction of groundwater and surface water, and temporal and geographical resolution.

The input, decisions, and points of discussion were compiled and brought back within the group of active members. The group is using the recommendations and works further on the harmonization of the points of disagreement. It is expected that a selection of indicators representing different ways to address the most important issues will be produced and tested in spring 2015. The analysis of the result should lead to a provisional recommendation by summer 2015.