Access to clean water and modern energy supply are key preconditions for modern life. Water-energy nexus refers to the tight interlinkage and high interdependence between water and energy demand and supply (WWAP, 2014). Energy production, especially hydropower and the cooling of thermal and nuclear power generation, depends on water. Reallocating water to different uses and places might increase the value per drop but increase energy use. Water supply, including water extraction, treatment, and distribution, requires significant energy use. In 2014, the global water supply’s energy use was 120 Mtoe, of which 60% was electricity, accounting for 4% of the worldwide electricity consumption (IEA, 2016).
In the urban context, water supply is typically sourced from groundwater or surface water from lakes or streams, treated, and distributed to end-users. Continued urbanization is driving both land area expansion and population increases in many cities, leading to increases in energy consumption and even energy intensity increase of urban water supply systems (Macharia et al., 2020; Huang et al, 2023).
The IEA projected a 16% increase in the global water demand of municipalities from 2015 to 2040. Such demand increase can lead to local water and electricity shortages, especially in developing country cities, due to ongoing climate change and its impacts on water availability, rapid urbanization, and per capita water consumption increase because of income growth (IEA, 2016).
As water is heavy, energy expenses are often a major operating cost component of urban water supply systems (UWSS) (Limaye & Jaywant, 2019). Leakage because of poorly maintained or not appropriately managed systems often incurs substantial water losses and, therefore, wastes the energy used for water supply. Applying the most efficient energy equipment in water supply systems and minimizing leakages are fundamental pillars to saving water and energy.
This issue brief focuses on the energy-water nexus in urban water systems, including urban water collection and supply systems. It will start with the opportunities for energy and water conservation in urban water supply systems, assess the challenges and options, and describe existing international support.
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