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Freshwater intensity

Plant-based ethanol, like most biofuels, requires a significant amount of water for production and processing, with irrigated feedstocks falling at the high end of use. Hydroelectric power plants also require significant amounts of water due to evaporation and subsurface seepage from reservoirs. Electricity generation requires large volumes of water for cooling, although gas-fired turbines are more efficient and require less water than coal-fired plants. Natural gas requires relatively little water to produce. This is true for conventional gas as well as shale or tight gas – the additional water needed during a one-time hydraulic fracturing operation makes little difference over the life of a well and uses thousands of times less water than what would be required to irrigate, harvest and process an equivalent amount of biofuel energy over the same time period. Oil sands and conventional oil are also comparatively light in their water requirements.