Water and energy are deeply interconnected in what scientists call the water-energy nexus. In the twentieth century alone, global energy use grew ten-fold while water use grew six-fold, and both continue to rise with population growth and increasing affluence. Understanding water use in electricity generation requires distinguishing between water withdrawal (water removed from a source) and water consumption (water that is evaporated, transpired, or otherwise not available for immediate reuse). Electricity is the fastest-growing form of energy, making water consumption across different generation methods—typically measured in liters per megawatt-hour (L/MWh)—a critical metric for sustainable energy planning.
The water intensity of electricity generation varies dramatically across different technologies. Wind and solar photovoltaic (PV) systems have the lowest water consumption because they require no cooling; their minimal water use occurs upstream during mining and manufacturing of components, plus occasional panel cleaning. In contrast, thermal power plants (coal, natural gas, nuclear, and biomass) require substantial water for cooling, depending on the cooling technology. Hydropower and biomass show the widest ranges: hydropower averages can appear high due to reservoir evaporation, while biomass water use depends heavily on whether feedstock crops are rain-fed or irrigated.
For thermal power plants, which account for over 70% of utility-scale electricity generation, the cooling system type is the primary determinant of water use. Once-through cooling draws water from rivers or lakes, passes it through the plant once, and returns it—resulting in high withdrawal but relatively low consumption. However, this method creates thermal pollution, returning water at higher temperatures that reduces oxygen levels and severely disrupts aquatic ecosystems. Wet cooling (recirculating) systems use cooling towers where heat dissipates through evaporation, reducing withdrawal but increasing consumption as water is lost to the atmosphere. Dry cooling systems use no water for cooling, relying instead on air conduction and convection, but they are more expensive and less efficient than wet systems.
Hydropower and biomass present unique water challenges. While water flowing through hydroelectric turbines isn't considered consumptive (it remains available downstream), large reservoirs significantly increase surface area and evaporation rates, creating consumptive losses that vary widely by location and climate. Similarly, biomass electricity consumes substantial water through crop irrigation, plant transpiration, and processing—with irrigated crops using dramatically more water than rain-fed alternatives. These site-specific factors make average water consumption estimates for both hydropower and biomass highly variable and context-dependent.
Even when water isn't consumed, energy production still impacts the environment. Thermal power plants using once-through cooling return warmed water to rivers and lakes, creating thermal pollution that degrades aquatic habitats. Nuclear plants are often sited near large water bodies specifically to access cooling water, concentrating environmental impacts in those ecosystems. As climate change intensifies droughts and water scarcity, the water-energy nexus becomes increasingly critical: choosing low-water technologies like wind and solar PV isn't just about reducing emissions—it's about building resilient energy systems that can operate sustainably in a water-constrained future.