This study focused on understanding what sector-region combinations could be targeted to reduce total city water footprints? We used multi-regional input-output analysis of direct and virtual water, across five Australian capital cities and their supporting regions. The key novelty of this study is the high spatial resolution policy-relevant sub-sectoral analysis to identify sector-region combinations to reduce city water footprints. Virtual water footprints were 8-10 times higher than direct water consumption (per capita) in all studied cities. Virtual water from outside the city boundary is almost 20 times higher than the virtual water sourced from within the city boundary in all studied cities. Water-efficiency programs can significantly reduce the virtual water footprints of the studied cities. This includes water-efficiency and recycling on farm, and in food processing (e.g. livestock feed growing, dairy cattle farming, vegetable growing and processing) in rural regions of New South Wales, Queensland, and Victoria. The results are relevant to strategic city water footprints reduction, sustainable sourcing and planning for future disturbance of product supply, and water-sensitive city developments considering both direct and virtual water flows.

This study reviewed nexus researches, synthesize and discuss insights, methodological practices, and future outlook of water-related energy consumption assessment of the food system. For the first time, the study assessed: (i) the trends and drivers of water-related energy research in different countries, (ii) how water-related energy in the food system is being evaluated (objectives & scale, study dimension & analysis focus, and methods) and (iii) the significance of food-system water-related energy in comparison with other sectors. Of 686 nexus studies undertaken since 1990, 104 studies (15%) quantified water-related energy. Studies have generally broadened in scope through time. The USA, China, and Australia have conducted most studies representing 23%, 17%, 15% of total respectively. A few of the identified major drivers in these countries leading water-related energy assessment are: providing optimal solutions and avoiding problem-shifting, analyzing the challenges and opportunities to reduce water-related energy, and exploring the energy-saving benefits by saving water. Of the 104 water-related energy studies, 65 articles (∼60%) related to the food system, focussed on the agriculture phase for irrigation energy consumption. Existing nexus studies often ignored other phases such as food processing and cooking, which are more energy-intensive. Over 50% of studies used material flow analysis to evaluate water-related energy in the food system. Few of the nexus studies evaluated inter-regional flows or changes through time. Absence of a comprehensive study of the entire food system, and wide variations in study system boundary and definitions, make it difficult to compare sectoral significance. However, the order of sectoral water-related energy consumption (from highest to lowest) identified as industrial, residential, agriculture, and water and wastewater service. Our review demonstrates a tremendous opportunity and need for an overarching framework to enable systematic evaluation and benchmarking of water-related energy consumption of the food system.