The International Energy Agency concluded that freshwater use is becoming an increasingly crucial issue for energy production around the world in its 2012 World Energy Outlook.
Between steam systems for coal plants, cooling for nuclear plants, fracking for natural gas wells, irrigation for biofuel crops, and myriad other uses, energy production consumed 66 billion cubic meters (BCM) of the world’s fresh water in 2010. That is water removed from its source and lost to evaporation, consumption, or transported out of the water basin — as opposed to water withdrawn, used, and then returned to its source for further availability, which is a far larger amount.

According to figures it shared with National Geographic, IEA anticipates this water consumption will double from 66 BCM now to 135 BCM by 2035 with most of the growth accounted for by coal and biofuels:
If today’s policies remain in place, the IEA calculates that water consumed for energy production would increase from 66 billion cubic meters (bcm) today to 135 bcm annually by 2035.
That’s an amount equal to the residential water use of every person in the United States over three years, or 90 days’ discharge of the Mississippi River. It would be four times the volume of the largest U.S. reservoir, Hoover Dam’s Lake Mead.
More than half of that drain would be from coal-fired power plants and 30 percent attributable to biofuel production, in IEA’s view. The agency estimates oil and natural gas production together would account for 10 percent of global energy-related water demand in 2035….
The surest way to reduce the water required for electricity generation, IEA’s figures indicate, would be to move to alternative fuels. Renewable energy provides the greatest opportunity: Wind and solar photovoltaic power have such minimal water needs they account for less than one percent of water consumption for energy now and in the future, by IEA’s calculations.

This presents a challenge, since river flows, aquifers, and other sources of fresh water are already being strained by the twin drains of population growth and less reliable rainfall due to climate change. The United Nations is projecting that by 2025, 1.8 billion people will live in regions with severe water scarcity, and two-thirds of the world’s population could be living under water-stressed conditions. Given water’s importance in different forms of energy production, this presents a double hit: Less available fresh water for human consumption, plus strained and costlier energy supplies