Water footprinting of agricultural products: evaluation of different protocols using a case study of New Zealand wine

Abstract

Abstract Globally, food industries are confronting the serious challenges associated with freshwater use. The water footprint (WF) is a metric that quantifies the potential environmental impact related to water. A number of methods for water footprinting have been proposed, while international standards are in the process of being developed. The water footprints of bottles of wine produced in two different regions of New Zealand were assessed using four water-footprinting methods: the consumptive use method of the Water Footprint Network (WFN), plus two recently proposed life cycle assessment (LCA) based methods and the hydrological water balance method. The outcomes of these methods were evaluated for their ability to indicate the local impacts on water resources and their usefulness to key stakeholders. The WF method of WFN quantifies the blue and green-water consumption, and further information on water resource availability is required to assess the impacts on local water resources. The grey-WF indicates the impact on water quality, and comparisons can be made between products, but the absolute values are less meaningful. The LCA based methods of the stress-weighted WF, freshwater ecosystem impact and freshwater depletion do indicate impacts. Also products from different locations can be compared. However, these indicators are limited in their ability to show local impacts because of constraints in their characterization factors. The WFN method and two LCA methods are based on consumptive water use. The water consumed through evapotranspiration, however, returns as precipitation within a reasonably short time and often at a local scale. So water footprinting based on water consumption alone is limited in terms of assessing the local impact of primary production on water resources. Furthermore, the applicability of the outcomes of these three methods to growers and resource regulators is not straightforward. The hydrological water-balance method indicates the impact on water quantity as a volumetric measure, so that it can be understood by the non-technical community. For the growers, it provides a sensible measure of the impact of their production, as well as useful information for setting measurable targets to reduce the WF. It can also be helpful for resource regulators to manage their water resources by matching water demand to water availability or replenishment. The robustness of the WF protocols for measuring the impact of product life cycle on water quality needs further improvement so that water footprinting can provide metrics of the sustainable use of our water resources.