Letter pubs.acs.org/est
Water Footprint: Pitfalls on Common Ground
B
oulay et al.1 highlight areas of common ground between the water footprint methodologies of the Water Footprint Network (WFN)2 and those based on LCA.3 We think that between the common ground are some important pitfalls which represent unsuspecting danger for policy makers and other end users of water footprint information. From a conceptual point of view, both methodologies might be adjusted to comply with the upcoming ISO 14046 standard on water footprint4 since both concepts agree on including water consumption and pollution. However, a major conceptual inconsistency relates to the inclusion of green water in the WFN approach, since it does not fully affect the water cycle and is rather an indicator of land use.3 Also the method for assessing green water scarcity published by Nunez et al.5 is not meant to be used for a water footprint. The second major issue is the combination of a hypothetical “pollution volume” (gray water) with water consumption volumes (blue water) for the water footprint. Such sums are not environmentally meaningful or informative for water resource managers, consumers or manufacturers/retailers wanting to make procurement decisions which lead to less pressure on water resources. An equivalent of a pollutant and water volume is not constant but location-specific and therefore needs consideration by impact assessment. Additionally, the threshold approach for assessing gray water has severe limitations: Variations in residence times in environment (decay and removal processes) are not considered and only a few pollutants can be addressed by this approach (many reports focus on Nitrogen only).6 While the LCA community has included the main developments of WFN publications, we rather see synergies to use the resources available from LCA research for updating WFN methodology regarding gray water and water scarcity related impacts to bring it into line with the requirements of the forthcoming ISO standards. Obviously for interpreting the water footprint results, available literature is enriching the communities and cross-fertilization is possible. Another shortcoming of the WFN footprint definition is that many results published based on this approach are not consistently following the respective guidelines.2 Often numbers are published aggregating green, gray and blue water. Regarding gray water studies mostly consider nitrogen emissions for agriculture while for industrial and domestic water the untreated water release is directly used as gray water volumewithout distinguishing pollution grades.7 Obviously, this procedure does not comply with the expectations toward a meaningful water footprint, and eventually leads to misinformation if resulting data is published without specifying such limitations, as e.g. done in the case of The Swiss Water Footprint Report.8 Finally, we do not see two different application situations for the methods as stated by Boulay and colleagues.1 Both approaches can report results from a product perspective as well as on regional level that can be used alongside other water resource management tools as the footprint concept contributes the supply chain perspective. Therefore, the upcoming ISO © 2013 American Chemical Society
14046 standard, which has not only a product focus, should be considered for overcoming current pitfalls and reporting a consistent water footprint.
Stephan Pfister*,† Bradley G. Ridoutt‡ †
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ETH Zurich, Institute of Environmental Engineering, 8093 Zurich, Switzerland ‡ Commonwealth Scientific and Industrial Research Organisation, Private Bag 10, Clayton South, Victoria 3169, Australia
AUTHOR INFORMATION
Corresponding Author
*Phone: +41-44-633-75-71; fax:+41-44-633-10-61; e-mail: pfi
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Boulay, A.-M.; Hoekstra, A. Y.; Vionnet, S. Complementarities of water-focused life cycle assessment and water footprint assessment. Environ. Sci. Technol. 2013, 47, 11926−11927. (2) Hoekstra, A. Y.; Chapagain, A. K., Aldaya, M. M. and Mekonnen, M. M. The Water Footprint Assessment Manual: Setting the Global Standard; Earthscan: London, UK, 2011. (3) Ridoutt, B. G.; Pfister, S. Global Environ. Change 2010, 20, 113− 120. (4) ISO, Draft International Standard ISO/DIS 14046: Water FootprintPrinciples, Requirements and Guidelines; International Organization for Standardization: Geneva, Switzerland, 2013. (5) Núñez, M.; Pfister, S.; Antón, A.; Muñoz, P.; Hellweg, S.; Koehler, A.; Rieradevall, J. Assessing the Environmental Impact of Water Consumption by Energy Crops Grown in Spain. J. Ind. Ecol. 2012, 17, 90−102. (6) Ridoutt, B.; Pfister, S. A new water footprint calculation method integrating consumptive and degradative water use into a single standalone weighted indicator. Int. J. Life Cycle Assess 2013, 18, 204−207. (7) Mekonnen, M. M.; and Hoekstra, A. Y. National Water Footprint Accounts: The Green, Blue and Grey Water Footprint of Production and Consumption; UNESCO-IHE: Delft, the Netherlands, 2011. (8) WWF. The Swiss Water Footprint Report: A Global Picture of Swiss Water Dependence; WWF Switzerland/Swiss Agency for Developmentand Cooperation (SDC): Zurich, Switzerland, 2012.
Received: November 29, 2013 Accepted: December 6, 2013 Published: December 17, 2013 4
dx.doi.org/10.1021/es405340a | Environ. Sci. Technol. 2014, 48, 4−4
