Water–Energy Nexus

Present day water and energy systems are tightly intertwined. Water is used in all phases of energy production and electricity generation. Energy is required to extract, convey, and deliver water of appropriate quality for diverse human uses, and then again to treat wastewaters prior to their return to the environment. Historically, interactions between energy and water have been considered on a regional or technology‐by‐technology basis. At the national and international levels, energy and water systems have been developed, managed, and regulated independently. Water and energy are critical, mutually dependent resources – the production of energy requires large volumes of water and water infrastructure requires large amounts of energy (Das 2017; Das and Cabezas 2018; EPRI 2011; USDOE 2014a, 2013a, b).

Water is required to generate energy: Thermoelectric cooling, hydropower, energy mineral extraction and mining, fuel production (including fossil fuels, biofuels, and other nonconventional fuels), and emission controls all rely on large amounts of water. In the United States, the thermoelectric generating industry is the largest withdrawal user of water. According to USGS (United State Geological Survey), 349 billion gallons of freshwater were withdrawn per day in the United States in the year 2005. The largest use, thermoelectric, accounted for 41% of freshwater withdrawn at 143 billion gal/day. However, freshwater consumption for thermoelectric purposes is low (only 3%) when compared to other use categories such as irrigation, which was responsible for 81% of water consumed.

• Water withdrawal: The total volume removed from a water source such as a lake or river. Often, a large portion of this water is returned to the source and is available to be used again.
• Water consumption: The amount of water removed for use and not returned to its source.

Water supply also requires energy use: A large amount of energy is needed to extract, convey, treat, and deliver potable water. Additionally, energy is required to collect, treat, and dispose of wastewater. In 2010, the US water system consumed over 600 billion kWh, or approximately 12.6% of the nation’s energy according to a study by researchers at the University of Texas at Austin. The study found water systems use about 25% more energy than is used for residential or commercial lighting in the United States.

Water and energy are both multifaceted issues with many variables impacting their supply, demand, and management. Lawmakers should consider the following variables which add complexity to the management of water and energy:

• Growing population: According to a 2012 United States Census Bureau projection, the US population could reach 400 million people by 2051. Population growth affects energy use through increases in housing, commercial floor space, transportation, and economic activity. The US Energy Information Administration (EIA) estimates that total electricity consumption will grow from 3841 billion kWh in 2011 to 4930 billion kWh in 2040, an average annual rate of 0.9%. With a higher generating capacity, the United States will require additional water withdrawals.
• Agriculture: Feeding a growing population may require greater agricultural water use. Agriculture accounts for approximately 37% of total freshwater withdrawals in the United States, and 81% of water consumption.
• Geographical water demand: Water supply and demand are not geographically linked. From 1990 to 2010, the second largest regional population growth, 13.8%, occurred in the west, which is one of the most water‐deficient regions in the United States. Additionally, water consumption in the western United States is much higher than other regions due to agricultural demands. It is estimated that it takes over one million gallons of water a year to irrigate one acre of farmland in arid conditions. In other words about 86% of irrigation water withdrawals were in western states in 2000.
• Climate change: Climate change could affect water supply and electricity use. Warmer or colder weather patterns could result in increases or decreases in energy use. Changes in precipitation in a region could increase or decrease the ability to store water, agricultural production and water use, and overall water supply.

States are beginning to assess their energy options and promote policies that allocate financial support to a diverse range of technologies to encourage responsible, sustainable energy production. States are also becoming aware of the limitations to accessible water, and as our energy demands grow, competition for water among municipalities, farmers, industrial, and power suppliers will increase. Water and energy are linked at both the supply side (electric generation and water/wastewater facilities) and the end‐use side (residential, commercial, industrial, and agriculture sectors) (Figure 9.6). In order to sustain energy production and a dependable water supply, the United States must gain a detailed understanding of the interdependencies of water and energy systems and balance the needs of all users. State lawmakers and constituents will be critical in this process given their responsibility formulating policy, convening stakeholders, facilitating negotiations, and ratifying reached agreements.

Flows of energy and water are intrinsically interconnected, in large part due to the characteristics and properties of water that make it so useful for producing energy and the energy requirements to treat and distribute water for human use. This interconnectivity is illustrated in the Sankey diagram in Figure 9.7, which captures the magnitude of energy and water flows in the United States on a national scale. As shown in the diagram, thermoelectric power generation withdraws large quantities of water for cooling and dissipates tremendous quantities of primary energy due to inefficiencies in converting thermal energy to electricity. The intensity of water use and energy dissipated varies with generation and cooling technology.

As the largest single consumer of water, agriculture competes directly with the energy sector for water resources. However, agriculture also contributes indirectly to the energy sector via production of biofuels. Both connections will be strained by increasing concerns over water availability and quality. In addition, water treatment and distribution for drinking water supply and municipal wastewater also require energy.

Significant aspects of water and energy flows do not appear in Figure 9.6. First, flows will change over time, and anticipated changes in flows are important to consider when prioritizing investment in technology and other solutions. Increased deployment of some energy technologies in the future, such as carbon capture and sequestration, could lead to increases in the energy system’s water intensity, whereas deployment of other technologies, such as wind and solar photovoltaics, could lower it. In addition, there is significant regional variability in the water and energy systems, their interactions, and resulting vulnerabilities. For example, producing oil and natural gas through horizontal drilling and hydraulic fracturing has the potential for localized water quantity and quality impacts that can be mitigated through fluid life cycle management. Large volumes of water produced from oil and gas operations in general present both localized management challenges and potential opportunities for beneficial reuse. The energy requirements for water systems also have regional variability, based on the quality of water sources and pumping needs.

Water availability will affect the future of the water–energy nexus. While there is significant uncertainty regarding the magnitude of effects, water availability and predictability may be altered by changing temperatures, shifting precipitation patterns, increasing variability, and more extreme weather. Shifts in precipitation and temperature patterns – including changes in snowmelt – will likely lead to more regional variation in water availability for hydropower, biofeedstock production, thermoelectric generation, and other energy needs. Rising temperatures have the potential to increase the demand for electricity for cooling and decrease the efficiency of thermoelectric generation, as well as increase water consumption for agricultural crops and domestic use. These changes and variations pose challenges for energy infrastructure resilience.

Water and energy needs will also be shaped by population growth and migration patterns, as well as changes in fuels used and energy technologies deployed. For example, projected population growth in the arid southwest will amplify pressure on water and energy systems in that region. Increased production of oil and gas may increase both localized demand for water and generation of produced water that requires management. According to EIA data, planned retirements and additions of electricity generation units and cooling systems will likely decrease water withdrawals, increase water consumption, and increase the diversity of water sources used. While many of the forces affecting the water–energy nexus are out of the federal government’s direct control, the future of the nexus hinges on a number of factors that are within the DOE’s scope of influence, including technology options, location of energy activities, and energy mix.

The decision‐making landscape for the nexus is shaped by political, regulatory, economic, environmental, and social factors, as well as available technologies. The landscape is fragmented, complex, and changing; the incentive structures are overlapping but not necessarily consistent. Water is inherently a multi‐jurisdictional management issue and is primarily a state and local responsibility. States and localities vary in philosophies regarding water rights. There is also variation across states in relevant energy policies, including renewable portfolio standards, regulation of oil and gas development activities, and regulation of thermoelectric water intake and discharge. Regulations for both oil and gas development and thermoelectric water use are currently undergoing substantial change. Energy for water is also the subject of policy activity at multiple scales, from appliance standards to municipal water treatment funding mechanisms. A more integrated approach to the interconnected energy and water challenges could stimulate the development and deployment of solutions that address objectives in both domains (Table 9.2; AGU 2012; Clark and Veil 2009; DOE 2013a, b; EPRI 2011).