Environmental and social life cycle assessment of urban water systems: The case of Mexico City.

Mexico City and its metropolitan area have suffered problems of sustainability in the water system. The main goals of this study were to assess the environmental and social impacts of the water system in Mexico City using Life Cycle Assessment (LCA), identify the significant impacts and their sources, and provide a new perspective for a sustainable water system in the city. The entire water system was considered, including the following stages: water abstraction and treatment, transport, distribution, use, sewage collection and wastewater treatment. Social Life Cycle Assessment was performed considering the UNEP/SETAC Guidelines for the Social-LCA of products and the water system workers. We used five subcategories (working hours, fair wage, health and safety conditions, social security and professional development) and 30 indicators of labor conditions. The results of LCA show that the processes of abstraction, water treatment, transport and distribution combined to produce between 83.9 and 89.6% of the impacts in four of six categories. However, the transportation stage generates the highest environmental impacts due to energy consumption. The wastewater treatment stage avoids environmental impacts in freshwater eutrophication (-69.9%) and non-carcinogenic effects (-86.2%) due to Atotonilco, the new centralized WWTP. The social life cycle assessment results indicated that the transport stage had the best social performance score, with a value of 0.3 on a scale of zero to one. The total system exhibited regular performance in health and safety conditions, with a value of 0.6 in this category. Moving toward a sustainable water system in Mexico City requires analyze future scenarios on the decentralization of potable water services and the implementation of renewable energy technologies in water abstraction and transport to reduce electrical energy consumption and mitigate global warming impacts. Regarding the social dimension, the water system requires stricter policies to monitor the health and safety conditions of workers according to the definition of decent work toward recent sustainable development goals. This study allowed us to identify the stages with high and low environmental impacts with LCA and, with S-LCA, the best and worst social performance in working conditions. The next step is to complete a sustainability assessment that includes the economic dimension, develop a framework to integrate the three dimensions and propose scenarios to improve environmental and social performance.