Interconnected Energy/Water Savings and Uses Worked Into Conservation Planning

Importance of energy/water nexus gaining recognition

by Joe Gelt

Just as producing energy consumes water, treating and distributing water requires energy. In other words, water is an energy issue; energy is a water issue. Called the energy-water nexus or connection, the interrelationship of energy and water is an issue getting increased attention.

Many people claim at least a general familiarity with the issue: mention the energy-water connection and they will likely think of dams generating hydroelectric power. The issue now claiming attention is much more complicated than that.

The second greatest U.S. water user after agriculture is the electricity industry. With its operations requiring a reliable, abundant and predictable water source, the industry consumes vast amounts of the resource. Producing electricity from fossil fuels and nuclear energy takes about 190,000 million gallons of water per day or 39 percent of all U.S. freshwater withdrawals. Of that amount, 71 percent goes to fossil-fuel electricity generation.

Considering the situation from the water side of the nexus, great amounts of energy are needed to ensure water supplies: as much 80 percent of the cost of water is attributable to energy costs for treatment and delivery.

Like groundwater and surface water, energy and water are interrelated issues. Understanding the workings of the nexus is critical to efforts at achieving either energy or water sustainability.

More Energy, More Water Needed

The energy/water nexus writ large. The decline in Lake Mead’s elevation since 1999 prompted the Bureau of Reclamation to initiate a program to modify the turbines at Hoover Dam to increase their electrical generating capacity at lower lake levels.

With energy and water demand expected to greatly increase in the future, some see a possible train wreck looming on the horizon. The 2001 National Energy Policy indicates that a growing population and expanding economy will require 393,000 megawatts of new generating capacity by the year 2020. This means 1,300 to 1,900 new power plants, more than one built each week.

Water supplies then become a critical issue to the power industry. Will a sufficient supply of dependable, affordable water be available to produce the energy to meet future needs? This may be problematic.

Population grows, energy demands increase, but freshwater supplies remain relatively constant. More people with more demands means less water to go around for generating energy and for other uses. Further complicating the energy-water situation is that population shifts and movements often occur without due regard to water availability. Areas of growing water demand may not be the same as areas where supplies are available.

For example, the 1990s saw the largest U.S. regional population growth, 25 percent, occurring in the mountain west, a region of generally scarce water resources. The same situation is occurring in the U.S. southeast: growing population, 14 percent since 1990, amidst increasing concerns about water availability. Meanwhile the northeast, which has a relative abundance of water, experienced only a 2 percent growth in population.

A growing population not only uses more electricity but also consumes more food, with the result that the two largest water users — energy and agricultural producers — will likely be competing for limited water resources. Both will need more water to serve additional customers.

In some situations environmental concerns about protecting fish and other aquatic organisms may restrict the amount of water available to generate electricity. Dam releases to benefit the environment may limit the generating capacity of a dam.

The workings of the nexus take on added complications when possible atmospheric effects are considered. Increasing electricity production will likely result in higher levels of atmospheric carbon. This in turn could affect precipitation in uncertain ways, possibly shifting patterns of existing water distribution. This could be to the disadvantage of electricity producers in certain areas.

The future scenario is increased energy needs in the face of limited water supplies. Where will the water come from needed to generate energy? With water scarcity boosting the cost of water, energy will become more expensive. How will more expensive energy affect the cost of water? The nexus bristles with interconnected complications.

Energy-Water Nexus Hits Home

National and regional energy and water trends and atmospheric phenomenon are parts of the big picture. But what about the smaller scale? For example, what significance, if any, does the energy-water nexus have to a family determined to save water? Such a family would need to develop interdisciplinary thinking skills, thinking about energy as well as water, to understand the full energy-water implications of conservation.
Coal is the most abundant fossil fuel, accounting for 52 percent of U.S. electricity generated; each kilowatt hour produced from coal requires a withdrawal of 25 gallons of water. Knowing one kilowatt hour of electricity = 25 gallons of water provides a standard for measuring water use in energy consumption. This information can help build consumer awareness that, like taking a shower or watering vegetation, operating a vacuum cleaner or air conditioner consumes water.

(The amount of water used to generate energy often escapes consumers’ attention, not only because it is usually a behind-the-scene, indirect use of water but also because a unit of energy is somewhat abstract, at least compared to water measured, for example, as gallons. Water used to generate kilowatt hours seems less tangible than water used to grow cotton or oranges.)

Energy Savings vs. Water Savings

Not heeding the energy-water nexus could result in a conflict between energy conservation and water conservation. In the fall/winter 2005-06 Water Conservation News, the California Urban Water Conservation Council described such a conflict. The council says consumers have been choosing different types of appliances in response to rapidly escalating energy prices. Some of these energy-saving appliances were developed and then purchased without consideration of water use.

For example, ice makers and home air-conditioners are at their energy-efficient best when using water to remove heat from the refrigerant in condenser coils. At one time, the high cost of water-cooled air conditioners discouraged homeowners from purchasing them. Increased electricity cost now justifies paying the high initial cost of the unit in expectation of down-the-line energy savings. What is occurring is a trade-off, with increased water consumption exchanged for energy efficiency

To add insult to injury the water consumption of the above energy-saving appliances peaks during the summer months, at a time when water suppliers are urging conservation. The council announced that it is consulting with the California Energy Commission to ensure that water gets due consideration when traded for energy conservation.

Conversely some efforts to save water have come at an energy cost. For example, a device that circulates water from hot water heater to tap ensures the availability of hot water as soon as the faucet it turned on. Water is thus saved but additional energy use results from the heat loss of the circulating water and the energy used to operate the pump.

Householders who install a low-flow shower head and are aware of the energy-water nexus realize they are reaping energy as well as water savings. A low-flow shower head saves water; using less water saves energy that would otherwise be used to heat additional water. Further, less water down the drain means less water to be treated, for an additional energy savings. It is a save-save situation.

Many of the scientific questions and technical challenges posed by the energy-water nexus have to do with finding ways to reduce water consumption when generating power, thereby lessening its effect on water quality and availability. Another concern is to reduce the amount of energy needed to treat and distribute water. The key to the quandary is an energy-water conservation strategy that mutually reduces consumption of both, rather than reducing the use of one at the expense of the other.

For example, efforts are underway to build more water-efficient power plants. Since power plant cooling consumes large quantities of water, a promising research track is to develop a cooling process that reduces or even eliminates water use. Other strategies include treating and using graywater in energy production or tapping into unused water sources such as saline aquifers.

Ways that are being considered to reduce energy use in treating, pumping and distributing water include improving wastewater treatment processes and refining irrigation technology.
Some complain of a dearth of resources to support energy-water research. They point out that while federal funding supports research of both energy and water sustainability, no national research program is devoted to understanding the interrelationship between energy and water.

The issue achieved some official recognition when Congress, as part of the Omnibus Spending Bill of 2005, funded the U.S. Department of Energy to develop a report on the interdependency of energy and water. In response to the directive, the DOE is compiling a National Energy-Water Roadmap Program.

The Sandia National Laboratories in New Mexico is a lead agency in the effort. Its energy-water nexus website (http://www.sandia.gov/energy-water/) provides a wealth of information on the issue as well as reports on the results of the three national workshops.

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