The Water Impact Index: a simplified single-indicator approach for water footprinting

Abstract

Purpose Along with climate change-related issues, improved water management is recognized as one of the major challenges to sustainability. However, there are still no commonly accepted methods for measuring sustainability of water uses, resulting in a recent proliferation of water footprint methodologies. The Water Impact Index presented in this paper aims to integrate the issues of volume, scarcity and quality into a single indicator to assess the reduction of available water for the environment induced by freshwater uses for human activities.Methods The Water Impact Index follows life cycle thinking principles. For each unit process, a volumetric water balance is performed; water flows crossing the boundaries between the techno-sphere and environment are multiplied by a water quality index and a water scarcity index. The methodology is illustrated on the current municipal wastewater management system of Milan (Italy). The Water Impact Index is combined with carbon footprint to introduce multi-impact thinking to decision makers. The Water Impact Index is further compared to results obtained using a set of three life cycle impact indicators related to water, from the ReCiPe life cycle impact assessment (LCIA) methodology. Results and discussion Onsite water use is the main contribution to the Water Impact Index for both wastewater management schemes. The release of better quality water is the main driver in favour of the scenario including a wastewater treatment plant, while the energy and chemicals consumed for the treatment increase the indirect water footprint and carbon footprint. Results obtained with the three midpoint indicators depict similar tendencies to the Water Impact Index. Conclusions This paper presents a simplified single-indicator approach for water footprinting, integrating volume, scarcity and quality issues, representing an initial step toward a better understanding and assessment of the environmental impacts of human activities on water resources. The wastewater treatment plant reduces the Water Impact Index of the wastewater management system. These results are consistent with the profile of the three midpoint indicators related to water from ReCiPe.

Simplified Direct Water Footprint Model to Support Urban Water Management

“…As such, it includes water balances at local level to support water management without addressing the consequences of water use in a more comprehensive water footprint sustainability assessment [12]. To better support informed decisions, recent scientific developments recommend adopting additional assessment such as the water scarcity or availability assessment [2,12,[38][39][40]. For example, Bayart et al [38] has presented the water impact index that allows the integration of consumptive and degradative water use of a process unit.…”

“…To better support informed decisions, recent scientific developments recommend adopting additional assessment such as the water scarcity or availability assessment [2,12,[38][39][40]. For example, Bayart et al [38] has presented the water impact index that allows the integration of consumptive and degradative water use of a process unit. The results are then characterized using a water scarcity index such as the one of Pfister et al [41].…”

“…Considering the outcomes of this study, future research can be planned as: (1) the development of a simplified water footprint sustainability assessment method to take into consideration also local water scarcity and availability as well as social and economic aspects [12,38]; (2) the application and possible adaptation of the proposed method at different levels, such as the regional one [42].…”

Life Cycle Impact Assessment

“…A slightly different approach including quality aspects is described in Bayart et al (2014): the water impact index (WII), which applies the WSI of to water quality classes, attributes lower CFs to consumption of polluted water quality classes. The issue of double counting arises in this approach too, but here the authors aim at covering an additional impact pathway on top of the pollution effect on ecosystem quality and human health: consuming high quality water and releasing lower quality water deprives further users of high quality water access, which is an effect not entirely covered by current impact assessment methods on emissions.…”

Life Cycle Impact Assessment

“…It should be noted that some midpoints also propose to include quality aspects, allowing the quantification of lower availability being caused by both consumptive and degradative use. This is either done through the use of water quality categories and the assessment of their individual scarcity (Boulay et al 2011), or through a distance-to-target approach, or dilution volume equivalent, in relation to a reference standard (Ridoutt and Pfister 2010;Bayart et al 2014).…”