Review of the water-energy-carbon nexus in small and medium drinking water systems: challenges and opportunities

Water is a critical resource for human life and plays a vital role in energy production. Energy is equally essential in water supplies but generates carbon emissions to the atmosphere depending on the energy source. Appraising water, energy, and carbon nexus is essential for promoting sustainable drinking water systems (DWSs) in the case of small- and medium-sized utilities, representing a significant portion of the water supply inmany countries. Smaller utilities face unique challenges, such as insufficient funding, aging infrastructure, and higher operational costs. This paper examines over 100 studies to identify and comprehensively understand how source type and location, raw water quality, water consumption patterns, system size, land use, population density, topography, infrastructure age, and system losses and maintenance impact energy consumption in small and medium DWSs. The review also identified more than 40 indicators related to energy and carbon from the literature, providing advanced information in this area. Findings suggest a gap in understanding how energy and carbon indicators relate to the utility's operational performance. By analyzing the challenges and opportunities smaller utilities face in optimizing water, energy, and carbon nexus, this paper highlights the necessity of shifting towards cleaner energy sources to mitigate the environmental impacts. It also emphasizes the importance of adopting a holistic approach that integrates technological advancements, regulatory guidelines, and active community engagement to achieve decarbonization in DWSs. The present study aims to inform policymakers, water management professionals, and broader stakeholders about the essential components of sustainable and resilient small and medium DWSs.