Grey Water Footprint Accounting, Challenges, and Problem-Solving

Abstract

Grey water footprint (GWF) is typically introduced as the environmental fraction of water footprint (WF). This indicator estimates the equivalent volume of freshwater required for assimilating the pollutants discharged by the production process to meet specific water quality standards. The conventional definition of GWF and its methodology for calculation is relatively simple and is initially introduced in this chapter. This indicator is then compared according to the global and national data of crops. Based on these evaluations, it is reported that the average GWF hardly exceeds 15% of the total WF of crops globally. Nonetheless, GWF and its ratio to the WFs of products is highly variable in different nations or regions, among different crops and products, and even between the same products with different production processes such as the rain-fed and irrigated crops. Therefore, this chapter later focuses on the challenges of GWF assessment. Here, the shortcomings are highlighted in the definition of GWF which may introduce some misunderstandings, particularly for water allocation. For example, it is pointed out that the ratio of GWF to crop WF is mostly influenced by a set of agriculture-related factors instead of environmental issues. This point in addition to the low ratio of GWF to WF implies that this indicator might be neglected in comparison with the blue and green WFs of crops. Another shortcoming is GWF uncertainties. This chapter also discusses the four pillars of uncertainty, with their related challenges and possible impacts on GWF assessment. For example, the different methods of water quality regulation may result in different GWF for a product. According to all these gap analyses, this chapter reintroduces the developed methodology for considering environmental concerns in GWF accounting and reinforcing its ecological role. A hypothesized study is chosen with some environmental issues to show how GWF problems can be solved by the altered methodology. Afterwards, the results are compared by which a conceptual model is developed for illustrating the impacts of a new accounting approach on intensifying the multiple-pollutant GWF of products. Finally, some research roadmaps emphasizing GWF and possible future trends are notified and recommended. © Springer Nature Singapore Pte Ltd. 2021.