It’s electricity that enables us to keep the lights on, the refrigerator and air-conditioner humming, and the television aglow. But there’s another critical resource that is quietly working behind the scenes of our daily power consumption … and that’s water.
Put another way: when you save electricity at home, you’re also saving water.
How so? Water is an indispensable operational ingredient at the vast majority of power plants in the United States. The more electricity that power plants produce, the more water they have to use.
In large part, we’re talking about the nation’s power plants that are coal-fired, burn natural gas, or use nuclear fuel. All of these “thermo-electric” power plants, which represent 86% of annual US electricity generation, work by producing intense amounts of heat and steam. And as part of this process, these facilities also need a reliable method to cool themselves off. The prevailing cooling method is water: on an average day, thermo-electric power plants in the US collectively withdraw 200 billion gallons of surface water (e.g. lakes, rivers, ocean), accounting for 53% of all surface-water withdrawals — as indicated in the below chart.
Source: US Geological Survey
Importantly, not all of the water that is withdrawn to cool off power plants is actually consumed. Rather, most of the withdrawn water is returned to its source. But a small amount of water in this process is indeed consumed (i.e. lost due to evaporation). The hydrological cycle does eventually bring the “lost” evaporated water back down to earth as precipitation. But where and when that happens is at nature’s whim, and cooling-water shortages in the interim have literally caused power plants to shut down (as recently as this past July during a Midwestern heat wave).
Power plants that run on hydropower (i.e. harnessing energy from swiftly flowing water, which accounts for 6% of US electricity generation) are similarly responsible for evaporative water losses. In fact, due to the large surface area of man-made reservoirs associated with hydroelectric dams, the amount of water lost in the electricity generation process is considerably higher for hydropower than for thermo-electric power.
How can we put in perspective the amount of water consumed by US power plants? Well, for every kilowatt-hour (kWh) of electricity generated, an average of 2 gallons of water is consumed. With respect to this post’s title: a US household’s big-screen TV runs on approximately 9 kWh per week, which corresponds to 18 gallons of water consumption at the power plant. In 2011, the US generated about 4.1 trillion kilowatt-hours of electricity (i.e. 4,106,000,000,000 kWh), so all that water consumption at thermo-electric and hydroelectric power plants can really add up.
The broader insight here is that energy and water — two resources that we couldn’t live without — are linked in deep ways that may not seem immediately apparent. And it’s not just that water serves an important role in how electricity gets made before it winds its way to our kitchens and living rooms. On the flip side, electricity is a key dimension of how water itself winds its way to our homes: consider, for example, that 8% of California’s total electricity consumption goes exclusively toward pumping water (including over mountain ranges) for delivery to customers across the state.
For more details on the strong connections between energy and water in our society and daily lives, see UC San Diego professor Tom Murphy’s recent analysis on his delightfully geeky blog, “Do the Math,” which inspired us to write this post.
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