Water–energy nexus for water distribution systems: a literature review

Water and energy are interdependent on each other. Energy is required to supply water to a system while, at the same time, water is needed for power generation in any natural or artificial system. This relationship is often called the water–energy nexus (WEN). In a water supply system, energy is consumed for source water extraction, transmission, treatment, and distribution. About 7%–8% of the world’s total generated energy is used for drinking water production and distribution. A major portion of this energy is used for distribution, i.e., pumping, chlorination, and maintenance activities, and hence is the focus of this review. Most of the world’s energy is generated by fossil fuels (oil, gas, and coal), which results in greenhouse gas (GHG) emissions. Here we review studies conducted to assess and evaluate the energy consumption and the related GHG emissions in water distribution systems (WDSs). This review covers the basic concepts and studies on WEN, energy saving solutions, renewable energy resources for water pumping, optimization of design, and the life cycle assessment (LCA) of large WDSs. Most of the reviewed studies suggest a trade-off between energy cost and the associated GHG emissions when selecting fixed-speed pumps over variable-speed pumps for large WDSs. To mitigate CO2 emissions, renewable energy resources like solar, wind, and mini-water turbines for water pumping have been discussed and mini-water turbines were found to be energy efficient solutions. The energy-focused LCA model has been studied to investigate the environmental impacts, GHG emissions, operational energy, and various life cycle stages of pipe manufacturing (embodied energy) in the network. Case studies of real world WDSs are reviewed and the potential research gaps are identified. Most life cycle studies have focused on the areas of pipe replacement, the life cycle cost of the system, the operational energy, and the reduction of GHG emissions, whereas less attention has been paid to the geographical and socio-economic issues along with the areas of human health, water resource diversity, and the hydraulic characteristics of WDSs.

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