Water–energy nexus in houses in Brazil: comparing rainwater and gray water use with a centralized system

The objective of this paper is to assess the potential for energy savings in water and sewerage services by means of on-site integrated water and sewage management strategies in low-income households in Florianópolis, Brazil. The on-site water efficiency measures include reclamation of gray water and rainwater use. The water and energy saving potential of both strategies were studied, and their energy intensities were compared to centralized water and sewerage services. Furthermore, the water consumption pattern for 10 low-income households was empirically determined using smart meters; the rainwater supply was estimated by using the computer program Netuno 4.0; and the water supply and sewage reduction potential of gray water systems were determined using a theoretical method. On average, the gray water and rainwater supply capacities were equivalent to 24% and 43% of the total water consumption of households, respectively. In regard to energy savings, rainwater harvesting was the most energy intensive strategy (0.86 kWh/m³), followed by centralized systems (0.84 kWh/m³); whereas, gray water was the most energy efficient strategy (0.54 kWh/m³). The findings suggest that alternative water and sewerage services may promote energy savings in comparison with centralized ones only when a concomitant reduction in sewage production is achieved.