Water Sustainability Index in the Billings Multiuse Reservoir: An Initiative for Studies of the Nexus Between Environment and Investments

The management of multipurpose reservoirs faces significant challenges due to conflicts between various demands, such as power generation, urban supply, irrigation, flood control, and environmental preservation. These conflicts result from the interdependencies between different sectors, which are often managed in isolation, making it difficult to implement integrated strategies. This chapter focuses on the Billings Reservoir, located in São Paulo, Brazil, which exemplifies the impacts of urbanization, pollution, and water regulation on the operational capacity of reservoir systems. Originally designed to store water for hydroelectric generation at the Henry Borden Hydroelectric Complex, the reservoir had its energy efficiency compromised by pollution from the Pinheiros and Tietê rivers. The analysis proposed in this study adopts the perspective of the water-energy-food (WEF) nexus, which seeks to balance the complex interactions between these interconnected demands. Using the dimensions of sustainability—environmental, social, economic, and technological—this chapter investigates how integrated water resource management can mitigate the impacts caused by the growth in demand for water, energy, and food, while promoting sustainable solutions. The application of the sustainability matrix provides essential support for the formulation of public policies and for decision-making by managers and regulatory agencies, assisting in investments for pollution control, in the allocation of resources, and in the definition of long-term strategies. Among the proposed solutions, the indirect potable reuse of treated sewage stands out as an alternative to increase water availability and improve water quality. In addition, this chapter emphasizes the need for investments in sanitation infrastructure and wastewater treatment technologies. Intersectoral cooperation, especially between the sanitation and energy sectors, is seen as crucial for efficient management of reservoir resources. In conclusion, the study reinforces that planning based on sustainability assessments is essential to ensure the efficient and balanced use of multiple-use reservoirs, such as Billings. The implementation of integrated models and the adoption of the nexus as a strategic tool not only strengthen the resilience of water systems, but also create opportunities to meet growing demands in a sustainable way, promoting environmental and socioeconomic benefits..