The Energy & Water Nexus

For decades, federal and state governments treated energy and water as two separate issues. It’s only been a relatively recent development that lawmakers and regulators have recognized the bond between energy and water and begun to take a more comprehensive approach in managing the resources. In fact, that recognition has given birth to an official name for the connection: the Energy-Water Nexus.

Unlike some pairings that can operate independently, energy and water are inextricably linked. It’s not a one-way street either: the treatment and delivery of water requires large amounts of energy, while, conversely, the generation of much of this country’s energy requires large amounts of water. This mutual dependence means that the supply and demand of one resource has a significant impact on the supply and demand of the other. It also means that governments and resource managers must take a holistic approach to their management in order to secure a sustainable future.

Let’s briefly look at how this energy-water codependence works. First, here are four ways in which water affects the generation or storage of electricity.

  • Direct power generation: Hydropower—electricity produced by the force of falling or moving water—accounted for 7% of all electric power generated in the United States in 2018, or 292 billion kilowatt-hours (kWh). Hydropower facilities can be found in 48 states and account for at least 10% of the electricity produced in 10 of those states, including California.
  • Indirect power generation: Nearly two-thirds of the electricity generated in the United States comes from nuclear, natural-gas, or coal-fired power plants that need water for cooling and the production of steam to drive turbines. Depending on the cooling system, a fossil-fueled or nuclear generating plant may require as much as 13 gallons of water to produce 1 kWh.
  • Fuel extraction and production: Pressurized water is a key ingredient in the process of extracting natural gas, coal, oil, and uranium that are used in power plants. Large amounts of water are also needed in the refining process for those fuels.
  • Pumped storage: In addition to generating electricity, water is also used to shift power to periods of peak demand. The United States currently has 6 gigawatts of pumped storage, in which water is pumped up to a high elevation at night (when demand is low) and released during the day to generate power when demand is high.

Turning the tables on this codependent relationship, here are four ways in which energy directly affects our water supply, delivery, and disposal system.

  • Pumping, treatment, and delivery: It’s estimated that 4–13% of the nation’s electricity generation is used to pump, treat, and deliver water. However, that number varies by region. In California, for example, the pumping, treatment, and discharge of water and wastewater account for as much as 19% of the state’s electricity consumption.
  • Water heating: Water must be heated to be effective for some end uses, so electric and natural-gas water heaters are needed to raise the temperature to appropriate levels. Water heating accounted for 12% of all U.S. residential electric use in 2018, or about 174 billion kWh. Water heating accounted for 9% of all nonresidential energy use, although that percentage is higher for businesses like restaurants, laundromats, hotels, and hospitals that require large amounts of hot water for dishwashing, clothes washing, and equipment sterilization.
  • Energy-intensive new technologies: As demand for water grows, especially in California, new technologies are being deployed to turn salt or brackish water into usable resources. While these technologies can help increase the water supply, they generally require more energy than what’s used to treat and deliver water from conventional sources.
  • Wastewater treatment: The energy-water connection doesn’t end with the customer’s use of the water. Once that water is used for bathing, dishwashing, or (ugh!) toilet flushing, it must be treated before it can be returned to the environment. In California, the process of treating 300,000 gallons of wastewater can take up to 1,400 kWh.

The tight-knit relationship between energy and water means that developments that affect one resource will also directly affect the other. For example, the severe droughts that California and other western states have experienced in recent years limited the amount of electricity that could be produced at hydroelectric facilities and constrained the operations of nuclear and fossil-fueled power plants that rely on large quantities of water for cooling and steam. On the other side of the coin, Superstorm Sandy knocked out much of the electrical grid in the New York-New Jersey area, resulting in an estimated 11 billion gallons of untreated sewage flowing into rivers, bays, streams, and city streets.

Fortunately, several positive developments on the horizon address the issue of tying our water supply system to our energy infrastructure.

  • Clean power: As more states follow California’s lead of mandating 100% clean energy by mid-century, wind and solar generation—which needs little or no water to produce power—will replace “thirsty” fossil-fuel power plants and free up water resources for more critical needs.
  • Water intensity decline: Although nuclear and fossil-fueled power plants continue to use vast quantities of water (52.8 trillion gallons in 2017), such facilities have dramatically reduced their volumes in the last few years. The amount of water needed to generate 1 kWh dropped from 15.1 gallons in 2014 to 13 gallons in 2017.
  • Water treatment efficiency improvement: With the energy needed for water treatment and delivery consuming as much as 30% of municipal energy bills, local water authorities are investing more in energy efficiency. Installing new, more-efficient pumping systems and controls—along with sensors to improve system automation—can produce energy savings of up to 20%.
  • Better policy coordination: Lawmakers and regulators have begun to understand that energy and water policies should be coordinated with each other, rather than addressed individually.

The bottom line is that what’s good for saving energy is also good for saving water—and vice versa. In fact, energy efficiency programs and water conservation programs can have a complementary effect on each other. A 2010 Pacific Institute analysis found that implementing a set of water conservation and efficiency measures that could reduce annual water use by 104.3 billion gallons could also save 2.3 billion kWh and 87 million therms of natural gas annually. The electricity savings alone are equivalent to the annual use of 309,000 typical California households.

Additionally, the California Energy Commission found that water efficiency improvements could save as much energy as some of the state’s existing energy efficiency programs do. Conversely, energy savings and their associated cost reductions can make many water efficiency measures cost-effective. For instance, front-loading clothes washers use about 35% less water than new, conventional washers do. But the water savings from these appliances—and their associated cost savings—may not be large enough to cover the washers’ higher prices. However, front-loading washers also produce significant energy savings because their lower water use translates to less energy needed to heat that water. The cost savings generated by the lower energy use can therefore make these washers very cost-effective.

By continuing to understand and appreciate the many ways in which energy and water are intertwined, government agencies can develop policies and implement programs that will lead to wise use of both precious resources.