Infographic: The Energy-Water Collision

Energy and water demands clash during hot, dry summers.

The Energy-Water Collision

Our power sector is built for a water-rich world. Conventional fossil-fuel and nuclear power plants require water to cool the steam they generate to make electricity. At some power plants, a lot of the water they withdraw gets evaporated in the cooling process; at others, much of the water is discharged back to its source (albeit hotter). The bottom line: Most power plants need a huge, steady supply of water  to operate, and in hot dry summers, that water can become hard to secure. 

The phrase “energy-water collision” refers to the range of issues that can crop up where our water resources and our power sector interact. This infographic illustrates the three main ways this problem occurs during hot, dry summers. Here are some recent examples of each type of problem:

  • Not enough water: Heat and drought in Texas in 2011 caused water levels in Martin Creek Lake to drop so low that Martin Creek Power Plant had to import water from the Sabine River to cool its coal-fired plant and keep it operating.
  • Incoming water too warm: During a 2006 heat wave, incoming Mississippi River water became too hot to cool the two-unit Prairie Island nuclear plant in Minnesota, forcing the plant to reduce output  by more than 50 percent.
  • Outgoing water too warm: To prevent hot water from doing harm to fish and other wildlife, power plants typically aren’t allowed to discharge cooling water above a certain temperature. When power plants bump up against those limits, they can be forced to dial back power production or shut down. Alabama’s Browns Ferry nuclear plant, on the Tennessee River, has done just that on several occasions in recent years — cutting its output three of the last five summers, for example, and for five consecutive weeks in one of those years (2010). Household electricity needs were met by other power generators, but at higher prices.   

As the map above illustrates, cases like these are cropping up across much of the country—and will likely become more frequent in the years ahead as temperatures increase and drought becomes more common.

Update: How Summer 2012 Strained the U.S. Power Sector

The extreme heat and drought that afflicted much of the United States during the summer of 2012 resulted in nearly a dozen new energy-water collisions, the most we have found in any of the years we have tracked. The majority were in the upper Midwest, where heat and drought were especially acute, with a couple of others taking place in the Northeast.

All of these new cases help shed light on how dependent our electricity system is on an adequate water supply, but some really showcase how far summer 2012 went in amplifying existing risks and exposing new ones:

  • Illinois: Four coal plants and four nuclear plants each sought and received “thermal variances” from the state to let them discharge hotter water than their permits allow, even amidst extensive heat-related fish kills and tens of millions of dollars in fisheries-related losses.
  • Vermont Yankee: In the first such case in northern New England, the Vermont Yankee nuclear plant was forced to reduce its power production over the course of a week by as much as 17 percent due to high water temperatures and low flow in the Connecticut River.
  • Millstone nuclear plant, Connecticut: In the case of Millstone, it was Long Island Sound that got too warm, forcing the plant to shut down one of its two reactors for 11 days in mid-July. This represents the first open-water collision on record and signals that even plants on large bodies of water are at risk as temperatures increase.


Information and data for this infographic were drawn from UCS analysis for the Energy and Water in a Warming World Initiative (EW3), including the recent reports Power and Water at Risk (2011) and Freshwater Use by U.S. Power Plants: Electricity's Thirst for a Precious Resource (2011).

UCS also offers the UCS EW3 Energy-Water Database for specialists and non-specialists to use for further research and analysis. The database is available as a downloadable Excel file. It is free and its use is unrestricted.

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Last revised date: September 27, 2012

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