The water-energy nexus in a drinking water supply system

The balance between water supply and demand is an essential issue, marked over time by political and environmental conflicts, as well as the impacts of natural disasters and the daily demand for several uses. The water issue is also mainstreamed by the United Nations that, in the “2030 Agenda for Sustainable Development”, included “Clean water and sanitation” between the 17 sustainable development goals. The balance between drinking water supply and demand implies the investment of resources aimed at optimizing resource management as well as proper understanding of the environmental consequences associated with techniques and operations implemented in a drinking water supply system (DWSS). With this goal, this study applies life cycle assessment (LCA) to a DWSS located in the Romagna region in Italy, with the aim to analyze the system and to compare, from an environmental perspective, three water sources namely dam water (RD), surface water (SW), and groundwater (GW), and two water purification technologies (i.e., conventional treatment and ultrafiltration). Identification and quantification of the main water and energy flows was achieved by applying material flow analysis (MFA) techniques, providing a scientific basis for the analysis of interlinkages between the water and energy in the regional context. 1 m3 of delivered drinking water was set as the functional unit, while system boundaries followed a cradle-to-gate approach. ReCiPe 2016 is applied as the impact assessment method. The LCA results showed the best environmental performance for RD water treated with the conventional technology, although the impact of dam infrastructure is greater than that of alternatives. GW is purified in conventional plants, but the high electricity demand of the withdrawal process makes this process the most carbon intensive. SW, instead, is affected by a significant amount of electricity required to pump water through the membranes in the ultrafiltration stage. Electricity dominates the potential contribution to fossil resources scarcity (71.0%), global warming (62.7%) and particulate matter formation (41.2%). Infrastructure is the main contributor to human carcinogenic toxicity (34.2%), followed by aluminum sulphate, aluminum chloride and electricity. Charcoal prevails for land use (28.4%), followed by sodium hypochlorite, and aluminum sulphate/chloride. Because DWSS is highly energy demanding, sensitivity analysis clearly points out a significant decrease of environmental impacts if higher shares of renewable sources are utilized in the electricity grid mix, marking a clear way for de-carbonization of DWSS. Water-energy interconnections provides more in-depth understanding of the water-for-energy and energy-forwater implications related to the provisioning of drinking water. Despite electricity consumption is a main contributing input to drinking water supply, the water sector is responsible for a limited portion of the regional electricity consumption (about 0.5% of the total generated). On the other hand, the volume of water involved in hydroelectric energy productions corresponds to the 83% of the system water inflow, disclosing an essential role water in the regional de-carbonization perspective. LCA, MFA and the nexus analysis confirm to be fundamental frameworks for system-thinking approaches, which may ultimately support decision-makers and local communities to the planning of strategies for optimized and long-term reliable access to natural resources, which represents one of the most urgent challenges to face in the coming years.