Decentralized rooftop and container agriculture using greywater and fog harvesting: a feasible strategy for water–food–energy security in mediterranean urban environments

Achieving the Sustainable Development Goals in urban environments, such as zero hunger and agriculture and food security, requires strategies that increase food and biofuel production without adding extra pressure on urban freshwater resources. This study aims to evaluate the feasibility of rooftop and container agriculture in Mediterranean urban environments using two alternative water sources, including domestic greywater and atmospheric fog harvesting. Maize and sunflower are studied as strategic multipurpose crops due to their suitability for selected systems, adaptability to urban microclimates, and double applications in food and biofuel production. The analysis includes an assessment of urban cultivation areas, fog harvesting potential, greywater quality, and selected crop water requirements, besides the importance of simultaneous consideration of food and energy security. Moreover, the detection methods for suitable areas, the potential rooftop and garden agriculture in some case studies, and the feasibility analysis of urban farming in rooftop and container agriculture using fog and greywater has been explored. Results indicate that domestic greywater, produced continuously within households, can satisfy the full irrigation demand for both crops across the entire growing season, while fog harvesting can supply a maximum value of 28% for sunflowers and 34% for maize water requirements. Moreover, the analysis determined that fog water is suitable for direct irrigation, whereas greywater may be used directly for biofuel-oriented agriculture or applied to food crops following a pre-treatment. In conclusion, the investigation demonstrates that combining fog harvesting with greywater reuse provides a practical and decentralized approach to support urban agriculture for multipurpose crops, enhance local food and energy resilience, and reduce dependence on potable-water networks.