This letter consists of a first-order analysis of the primary energy embedded in water in the United States. Using a combination of top-down sectoral assessments of energy use together with a bottom-up allocation of energy-for-water on a component-wise and service-specific level, our analysis concludes that energy use in the residential, commercial, industrial and power sectors for direct water and steam services was approximately 12.3 ± 0.3 quadrillion BTUs or 12.6% of the 2010 annual primary energy consumption in the United States. Additional energy was used to generate steam for indirect process heating, space heating and electricity generation.

The United States (US) energy system is a large water user, but the nature of that use is poorly understood. To support resource comanagement and fill this noted gap in the literature, this work presents detailed estimates for US-based water consumption and withdrawals for the US energy system as of 2014, including both intensity values and the first known estimate of total water consumption and withdrawal by the US energy system. We address 126 unit processes, many of which are new additions to the literature, differentiated among 17 fuel cycles, five life cycle stages, three water source categories, and four levels of water quality. Overall coverage is about 99% of commercially traded US primary energy consumption with detailed energy flows by unit process. Energy-related water consumption, or water removed from its source and not directly returned, accounts for about 10% of both total and freshwater US water consumption. Major consumers include biofuels (via irrigation), oil (via deep well injection, usually of nonfreshwater), and hydropower (via evaporation and seepage). The US energy system also accounts for about 40% of both total and freshwater US water withdrawals, i.e., water removed from its source regardless of fate. About 70% of withdrawals are associated with the once-through cooling systems of approximately 300 steam cycle power plants that produce about 25% of US electricity.

Electricity generation often requires large amounts of water, most notably for cooling thermoelectric power generators and moving hydroelectric turbines. This so-called "electricity-water nexus" has received increasing attention in recent years by governments, nongovernmental organizations, industry, and academics, especially in light of increasing water stress in many regions around the world. Although many analyses have attempted to project the future water requirements of electricity generation, projections vary considerably due to differences in temporal and spatial boundaries, modeling frameworks, and scenario definitions. This manuscript is intended to provide a critical review of recent publications that address the future water requirements of electricity production and define the factors that will moderate the water requirements of the electric grid moving forward to inform future research. The five variables identified include changes in (1) fuel consumption patterns, (2) cooling technology preferences, (3) environmental regulations, (4) ambient climate conditions, and (5) electric grid characteristics. These five factors are analyzed to provide guidance for future research related to the electricity-water nexus.

We utilize a unit commitment and dispatch model to estimate how water use fees on power generators would affect dispatching and water requirements by the power sector in the Electric Reliability Council of Texas' (ERCOT) electric grid. Fees ranging from 10 to 1000 USD per acre-foot were separately applied to water withdrawals and consumption. Fees were chosen to be comparable in cost to a range of water supply projects proposed in the Texas Water Development Board's State Water Plan to meet demand through 2050. We found that these fees can reduce water withdrawals and consumption for cooling thermoelectric power plants in ERCOT by as much as 75% and 23%, respectively. To achieve these water savings, wholesale electricity generation costs might increase as much as 120% based on 2011 fuel costs and generation characteristics. We estimate that water saved through these fees is not as cost-effective as conventional long-term water supply projects. However, the electric grid offers short-term flexibility that conventional water supply projects do not. Furthermore, this manuscript discusses conditions under which the grid could be effective at "supplying" water, particularly during emergency drought conditions, by changing its operational conditions.

Intra-national electricity transmission drives virtual water transfer from electricity production regions to electricity consumption regions. In China, the water-intensive thermoelectric power industry is expanding quickly in many water-scarce energy production hubs in northern and northwestern provinces. This study constructed a node-flow model of inter-province electricity transmission to investigate the virtual water and scarcity-adjusted virtual water (or virtual scarce water) embodied in the electricity transmission network. It is revealed that total inter-provincial virtual water transfer embodied in electricity transmission was 623 million m 3 in 2011, equivalent to 12.7% of the national total thermoelectric water consumption. The top three largest single virtual water flows are West Inner Mongolia-to-Beijing (44 million m 3), East Inner Mongolia-to-Liaoning (39 million m 3), and Guizhou-to-Guangdong (37 million m 3). If the actual volumes of consumptive water use are translated into scarcity-adjusted water consumption based on Water Stress Index, West Inner Mongolia (81 million m 3), Shanxi (63 million m 3) and Ningxia (30 million m 3) become the top three exporters of virtual scarce water. Many ongoing long-distance electricity transmission projects in China will enlarge the scale of scarce water outflows from northwestern regions and potentially increase their water stress.

Hydraulic fracturing faces several environmental challenges: the process is highly water-intensive, generates significant volumes of wastewater, and is associated with widespread flaring of coproduced natural gas. One possible solution to simultaneously mitigate these challenges is to use energy from flared natural gas for on-site wastewater treatment, thereby reducing flared gas, volumes of wastewater, and volumes of freshwater necessary for subsequent shale production as treated wastewater could be reused. This study builds an analytical framework for understanding the feasibility of this approach. We concluded that the thermal energy required to treat wastewater from the first 10 days after well completion is 148000–865000 MJ (140–820 MMBTU) and would generate 750–6800 m3 of treated water. Additionally, using the volume of flared natural gas in Texas in 2012, the theoretical maximal volume of treated water that could be generated was calculated to be 180–540 million m3, representing approximately 3–9% of the state’s annual water demand for municipal purposes or 1–2.4% of total statewide water demand for all purposes (Water for Texas: 2012 State Water Plan; Texas Water Development Board: Austin, TX, 2012).

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This study characterizes cooling water sources (by type and quality) and cooling water usage rates in thermoelectric power plants across the US based on data reported by power plant operators to the Energy Information Administration (EIA) for the year 2014. Geospatial distributions of water usage by specific cooling technologies and water sources confirm trends towards wet recirculating cooling systems, dry cooling and reclaimed water usage in the power sector, especially in more water constrained locations. Results include a database of water withdrawal and water consumption rates for 672 unique power plants organized by fuel, prime mover and cooling system classification, expanding available data records by an order of magnitude from previous analyses. While median calculated rates are generally comparable to values reported in the literature for most cooling technologies, results suggest that water usage rates at power plants with unique locations or operating conditions might not be accurately characterized by averages, especially in the case of once-through cooled facilities. Despite previous criticisms of EIA cooling water data, improvements in form instructions, reporting methods, and cooling system definitions have markedly improved the quality and usability of cooling water data records in recent years.