Water footprint assessment for water stewardship in the agri-food sector

The water footprint assessment framework aims to illustrate the full impact of water consumption in the whole life cycle of a product, from direct water extraction to water pollution. The framework provides a comprehensive indicator for water resources which, if used with care, can provide detailed information about the different impacts of water consumption in order to aid with water stewardship in the agri-food sector. However, the framework suffers from considerable uncertainties caused by discrepancies in the selection of critical limit values, leaching fractions or models and defining the scale of the study. A case study of oat farming in southwestern Finland and two oat products, oat flakes and an oat drink, is used to illustrate difficulties and opportunities in the application of the framework. The water footprint accounting is done with an applied leaching model and watershed specific nutrient limits for Finland in order to show the importance of the selection of critical parameters. Especially the grey water footprint, a measurement of water pollution and serves as an indicator for water quality, is emphasized as a crucial component in the total embedded water of agri-food products. In this study phosphorus was selected as the critical nutrient in the grey water footprint calculations. Moreover, an alternate impact assessment deviated from the one presented in the water footprint manual is suggested to better illustrate the changes in assimilative capacity of the selected water body. The water footprint of oat is, in this study, calculated to be highly variable depending on the chosen watershed, the leaching model or fraction, and the natural and maximum phosphorus concentrations defined. The study shows that the water footprint assessment framework can only become valuable as an indicator if the parameters used are carefully selected, while reliable benchmarking can only follow if the parameters are standardized. If the assumptions and methodology used are clearly defined from the onset of the assessment, the framework can serve as a useful internal indicator to show trends in water use and quality. Finally, the study illustrates the importance of considering diffuse pollution when planning water stewardship in the agri-food sector.