Transporting Water

Localized water constraints necessitate transporting water farther from its source to end use. Common proposals include long-haul pipelines and interbasin transfer, which moves water from one river basin to another. While aqueducts have transported water for thousands of years, the scale, length, and volumes of water transportation projects continues to increase. Some of the classic water transfer systems include the State Water Project in California, which is the single largest consumer of electricity in the state. The energy is consumed from pumping water over mountains, though some of the energy is recaptured as the water flows back downhill through inline hydroelectric turbines coupled with chutes.

Watch a 1964 presentation on the North American Water and Power Alliance, which would have transferred 93,000 m³ (24.6 million gallons) of water from Canada to the United States. Environmental and economic concerns made the plan unpopular with many groups.

As water tables fall and surface sources dry up, municipalities are more likely to consider the cost of expensive and far-flung water gathering systems that pull water to a city from deeper in the ground or farther away. Generally, long-haul systems will rely on energy-intensive pumps rather than gravity and introduce ecosystem impacts as water leaves one basin and enters another. Interbasin transfer permanently removes water from one basin and may enable invasive species to enter new environments.

China’s ambitious South-North Water Transfer Project will move 44.8 billion m3 (11.8 trillion gallons) of water per year from relatively water-rich southern China to the relatively water-poor north.

The South-North Water Transfer Project in China, also known as the South-to-North Water Diversion Project (SNWDP), ambitiously proposes to move major southern rivers—the Yangtze and Han Rivers—across the country to the Yellow and Hai Rivers. In theory, water-rich southern China could quench the thirst of the water-poor industrialized north. Projections estimate the Chinese endeavor will divert 44.8 billion cubic meters (m3) (11.8 trillion gallons) of water per year for a total capital cost of $62 billion. However, this estimate excludes the ongoing marginal energy costs of maintaining the pipeline and pumping infrastructure and the electricity necessary to pressurize and pump the water. China isn’t the only country with ambitions for global-scale water infrastructure. For decades, U.S. water planners have proposed diverting the Yukon River in Alaska or the Missouri River to the Southwest, so that the deserts would bloom with flowers and fruit trees. In Texas, a 386-kilometer (240-mile) pipeline will transfer 370,000 m3 (100 million gallons) of water per day from Lake Palestine to the Dallas/Fort Worth Metroplex. The plan estimates the total capital costs of construction at $888 million, or $2.3 million per kilometer ($3.7 million per mile) of pipeline, and an annual electricity consumption of $11.3 million, or $0.71 per cubic meter.

A worker prepares to bury a section of the Integrated Pipeline Project, which when finished will supply Dallas and Fort Worth, Texas, with about 370,000 m3 (100 million gallons) of water per day.

Image Credits: kenkistler/; Nsbdgc/CC BY-SA 4.0; Tarrant Regional Water District/.


Desalination is the process of desalting water, either by removing the salt from the water or removing the water from the salt. Thermal systems and membrane systems provide about 95% of all desalination globally, with other minor approaches such as freezing and electrodeionization providing the remaining 5%.1Global Water Intelligence, Desalination Markets 2010: Global Forecast and Analysis (Oxford: Global Water Intelligence, 2010). Thermal systems include processes such as boiling water, which separates out the salts by evaporating the water and condensing the subsequent vapor, leaving the salts behind. While effective, this system consumes more energy than other methods. For example, multi-stage flash systems use a series of steps and pressure drops to evaporate water, and multi-effect distillation reuses energy from a previous stage. Thermal approaches have low efficiency in practice, but because they can use waste heat as the source they can be integrated into large facilities with abundant waste heat, such as power plants, improving overall efficiency.

The Wärtsilä Serck Como multi-stage flash (MSF) evaporator produces fresh water from seawater, well water, or industrial water. Naval vessels and cruise ships typically use units like these to provide fresh water on board.

Membrane systems use a semi-permeable barrier to filter out dissolved solids. The most popular membrane approach is reverse osmosis. Other membrane approaches include forward osmosis, nanofiltration, and electrodialysis. Reverse osmosis filters use electrically driven pumps to push water through membranes that act as a filter to separate out the salts. The membranes separate two streams of water with different levels of salinity. Normally, osmotic pressures drive salts from the side with greater salinity toward the side with lower salinity to achieve equilibrium. However, the pumps reverse this flow, causing the salty side to get saltier and the fresh side to get less salty. Reverse osmosis systems are generally more energy-efficient than boiling water, but are expensive technologies that require electricity as opposed to just heat.

Reverse osmosis systems pump high-pressure saline water through membranes that act as a filter to separate out the salts.

Image Credits: Zern Liew/

Clean Water

Stricter water and wastewater treatment standards, deeper aquifer production, long-haul pipelines, and desalination each contribute to more energy consumed in the pursuit of water. Protecting drinking water quality from the output of water treatment plants for the sake of public health and discharge water quality from wastewater treatment plants for the sake of ecosystems requires nontrivial amounts of energy. As standards for water and wastewater treatment tighten, energy consumption for water treatment increases. While efficiency of new treatment technologies and methods increases over time, standards usually tighten in parallel.

Simultaneously, water entering water and wastewater treatment plants becomes more polluted with time. As the population grows, discharges into waterways increase while the purity of that water decreases. For example, concerns grow about pharmaceuticals (including birth control hormones and narcotics) in sewage streams, which require new equipment and ongoing investments of energy and capital to remove from wastewater.1David Sedlak, Water 4.0: The Past, Present and Future of the World’s Most Vital Resource (New Haven: Yale University Press, 2014). Increased biofuels production from corn ethanol in the United States causes additional runoff of nitrogen-based fertilizers and other pollutants, requiring more energy to clean the water downstream. 2K. M. Twomey, A. S. Stillwell, and M. E. Webber, “The unintended energy impacts of increased nitrate contamination from biofuels production,” Journal of Environmental Monitoring 12 (2010), 218-224. If pollution infiltrates the groundwater, as has happened in the Corn Belt, homesteads that rely on personal wells might require treatment systems, increasing their energy consumption for their water.

Wastewater streams from hydraulic fracturing of shales contain much higher levels of total dissolved solids than most wastewater treatment plants can handle.3B. D. Lutz, A. N. Lewis, and M. W. Doyle, “Generation, transport, and disposal of wastewater associated with Marcellus Shale gas development,” Water Resources Research 49 (2013), 647–656.Disposal requires energy to remove wastewater to disposal sites or specialized industrial wastewater treatment facilities at a great distance, to recycle and reuse the water in subsequent wells on site, and to treat the wastewater with new equipment.

Image Credits: PhotoSky/


In the traditional hydrosphere, freshwater rivers flow from their headwaters into the ocean, releasing potential gravitational energy along the way. In seawater desalination, the process is reversed. Producers pull saltwater from the ocean, invest energy, and produce freshwater, which is then pumped uphill for use in built environments. As of 2010, nearly 17,000 desalination plants provided approximately 68 million cubic meters (m³) (18,000 million gallons) per day of freshwater.1. Global Water Intelligence, Desalination Markets 2010: Global Forecast and Analysis (Oxford: Global Water Intelligence, 2010).Economists project the capacity to keep growing. While thermal desalination (using heat) represented about 25% of the installed capacity by 2010, this method represented a shrinking share of new installations, as builders sought the less energy-intensive reverse osmosis membrane-based system. Even the lower-energy approach consumes an order of magnitude more energy than traditional freshwater treatment and distribution. In addition to energy intensity, desalination infrastructure requires massive capital investments. In 2010, the global market approached $6 billion, and analysts predict the market to reach $18 billion in 2016.

Desalination growth is centered in energy-rich, water-poor regions of the world, such as the Middle East, northern Africa, and Australia. After a severe drought that lasted several years, water-strapped Israel turned to the sea for its freshwater, rapidly building a handful of desalination plants to produce about 200 billion gallons (760 million m³) of freshwater annually by desalinating water from the Mediterranean. 2Isabel Kershner, “Aided by the Sea, Israel Overcomes and Old Foe: Drought,” New York Times, May 29, 2015.Booming industrial activity in China is straining water supplies that serve the world’s largest population and is spurring rapid growth in desalination there. Recently, desalination capacity is also growing in locations such as London and the United States, where the abundance of water is very different than in the arid regions of the world.

While the cumulative installed desalination capacity continues to increase, the rate at which new projects come online has slowed from 2010 to 2016.

Despite relative water wealth, the United States is the world’s second-largest market for desalination, trailing only Saudi Arabia.3Global Water Intelligence, Desalination Markets 2010: Global Forecast and Analysis (Oxford: Global Water Intelligence, 2010). Unequal distribution of water resources, high per capita water consumption, and readily accessible capital for investments spur the development of desalination in the United States. Companies and cities in California, Texas, and Florida are considering projects for seawater reverse osmosis. Inland Texas, Arizona, and New Mexico are also home to brackish water projects.

When necessary, water solutions can combine desalination and long-haul transfer requiring even larger investments of energy.4 A. S. Stillwell, C. W. King, and M. E. Webber, “Desalination and Long-Haul Water Transfer as a Water Supply for Dallas, Texas: A Case Study of the Energy-Water Nexus in Texas,” Texas Water Journal 1 (2010), 33-41.Gravity pulls water to the sea naturally. Coastal waters at sea level require pumping water uphill to cities. For example, a planned project to move water from a coastal facility along the Gulf of Mexico to San Antonio, Texas, requires piping water 150 miles (240 kilometers) inland, increasing in elevation nearly 775 feet (235 meters). Freshwater scarcity and energy abundance in places such as the Middle East or Libya overcome the environmental and financial drawbacks of desalination. However, in places such as the United Kingdom or the United States will benefit from other cost-effective options such as water conservation, gray water capture, and water reuse.

The Claude “Bud” Lewis Carlsbad Desalination Plant is a 189,000 cubic meters (50 million gallon) per day seawater desalination plant located adjacent to the Encina Power Station in Carlsbad, California.

Energy of Bottled Water

Every step involved in producing bottled water—from treating the water, making the bottles, and shipping it to its final desintation—requires energy, and both the water’s quality and its location affect the amount of energy embedded in the process. For locally sourced bottled water, producing the bottle itself outweighs other energy requirements. However, long-distance transportation increases energy requirements substantially. Other energy requirements include those for processing, bottling, sealing, labeling, and refrigerating. 

Bottled Water



Locally Produced
Bottled Water






Energy Requirements for Producing Bottled Water

The bottle is just the beginning …

The vast majority of single-use plastic water bottles are made from a thermoplastic polymer resin. Combining the estimate of the energy required to make the plastic and to form it into bottles with the average weight-to-volume ratio results in a manufacturing energy cost of around 4.0 MJ per 1-liter bottle. This estimate includes the energy required to convert raw materials into resin, the energy required to turn resin into bottles ready for filling, and the energy required to transport bottles to the filling plant.

… but transportation is the biggest impact on embedded energy.

Purified water sourced and bottled within 200 km of the store and delivered by truck has a total transportation energy cost of around 1.4 MJ per liter. French spring water shipped by truck from the source to French ports, by ship across the Atlantic, by train from the East Coast of the United States to Los Angeles, and then locally by truck has a transportation energy cost of around 5.8 MJ per liter. 

Source: P H Gleick and H S Cooley, “Energy implications of bottled water,” Environ. Res. Lett. 4 (2009)

Image Credits: warloka79/; Jeffrey M. Phillips/Webber Energy Group.


Usually water for irrigation does not require treatment beyond simple filtering. Power plants treat water to prevent minerals from accumulating inside equipment but do not need water to meet potable standards. Some specialized industrial facilities, such as semiconductor fabrication plants, need energy-intensive ultrapure water. Drinking water for municipal systems needs to meet exacting standards, which usually requires extensive treatment. Then, after use in homes or businesses, water requires additional treatment to raise it to a standard that will not cause damage to the ecosystem. Water’s full supply chain in municipal settings includes pumping and conveyance from the original water source, water treatment, water distribution, end use, wastewater collection, wastewater treatment, and discharge.

The Ullrich Water Treatment Plant in Austin, Texas, uses energy and chemicals to treat and distribute water to customers. The water is pumped from a surface source (the Colorado River) to the treatment plant, which sits at a much higher elevation, after which the water flows to homes and businesses by gravity. Pumps, mechanical devices, and chemicals used to treat water to potable standards all require energy.

In addition to energy required to transport water to treatment plants, the treatment processes themselves require energy for pumping, blowing, aeration, ultraviolet (UV) lamps, and stirring. Chemicals used for treatment also contain embedded energy.

The amount of energy needed to treat water and wastewater to a suitable quality depends on the level of contamination, the nature of contamination, the water’s end use, and the physical features and treatment approach of the facility. Dirtier or contaminated water generally requires more energy for treatment, and end uses that require high standards of cleanliness also need more energy. Hospitals, semiconductor clean rooms, and food preparation facilities need water that is much cleaner than what is required for cooling industrial equipment or irrigating farms.

Silicon wafers being prepared for chip production. To manufacture integrated circuits on a 300 mm wafer requires approximately 8,330 liters (2,200 gallons) of water in total, of which 5,700 liters (1,500 gallons) is ultra-pure water (UPW). A facility may use between 7.6 and 15.1 million liters (2 to 4 million gallons) of UPW every day, which is approximately equivalent to the water use of a city with a population of 40 to 50 thousand people. 

Image Credits: Peter de Kievith/; RaJi/

Ocean Energy

Wave Energy

Global winds drive continuous waves with a force that beachgoers would easily recognize as powerful and unstoppable. Designs to capture this energy include Space Age-looking devices such as buoys with pistons inside that float up and down, gates that rock back and forth on the ocean floor, snake-like contraptions that twist with the waves, and turbines mounted inside tubes at the ocean’s edge that spin back and forth as water rushes in and out. The total resource is large and global, but expensive to harness, as the waves themselves damage or corrode equipment. Ultimately, capturing wave energy as a power source will include lining ocean coasts with hundreds of miles of power plants, a feat likely implausible given concerns about the possible impacts to the marine environment.

The Azura wave energy converter (WEC) is a one-of-a-kind, wave energy device designed to generate electricity from the motion of the choppy waters at the U.S. Navy’s Wave Energy Test Site in Kaneohe Bay on Oahu, Hawaii.

Tidal Energy

The moon’s gravitational pull raises the oceans several feet twice daily in cycles known as tides. Harnessing tidal energy requires technology similar to that used in conventional hydropower, so this resource is reliable, simple, and renewable. However, the availability of falling water and the requirements of large elevation gain between low tide and high tide limit the true feasibility of harnessing tidal energy. Optimal conditions exist in a few places around the world—Nova Scotia and northern France are two famous sites. In total, estimates for tidal capacity range from 3 to 4 terawatts (TW) of total power, which is big enough to make a difference, but not big enough to satisfy the globe’s total rate of energy consumption.

Ocean Thermal Energy Conversion

Another ocean-borne design known as ocean thermal energy conversion (OTEC) uses temperature differences between the relatively warm ocean surface (heated by the sun) and the cold ocean depths to drive a power plant. Unfortunately, because the temperature differences are small, these systems are plagued by low efficiency.

Makai Ocean Engineering’s Heat Exchange Test Facility opened in July 2011 and was designed for R&D and expansion. By adding a turbine and generator the facility, electrical power can be provided to the grid, and operation and control procedures can be perfected before creating a full-scale OTEC plant.

Salinity Gradients

Just as thermal gradients can be used to make electricity with OTEC, differences in salinity at the mouth of rivers where freshwater mixes with the ocean can generate electricity as water flows across osmotic membranes. While promising, early Norwegian experiments generated only enough power for a lightbulb. Undeterred, in late 2014 a Dutch team announced a trial of similar technology with the hope of making it economically feasible by 2020.1Toby Sterling, “Dutch seek to harness energy from salt water mix (Update),” PhysOrg, November 26, 2014, accessed August 27, 2016, link; and Sonal Patel, “Statkraft Shelves Osmotic Power Project,” Power Magazine, March 1, 2014, accessed August 27, 2016, link.Like OTEC, salinity gradient systems are also challenged with low efficiency.

Image Credits: Zacarias Pereira da Mata/; U.S. Department of Energy/public domain; NEHLA/Makai Ocean Engineering.

Energy From Falling Water

Globally, hydroelectric power accounts for over 16% of electricity generation worldwide. 1International Energy Agency, World Energy Outlook 2013 (Paris: Organization for Economic Cooperation and Development, 2014).Its water-use implications differ significantly from those of thermal generation because hydroelectric power does not withdraw or consume water for cooling. Instead, hydroelectric facilities leverage the sun’s energy, which lifts water to great heights through evaporation, and the force of gravity as the water travels back to sea level. A dam creates a large reservoir of water with a significant elevation differential. The elevation difference between the water behind the dam and the river downstream creates potential energy that can be converted to mechanical energy from rotating turbines. Hydroelectric turbines spin around a vertical axis like a carousel to spin magnets within an electrical generator.The simple design of a hydroelectric dam allows for 90% or higher conversion efficiency from the potential energy of the elevated water to electrical energy at the power house.2U.S. Army Engineer Institute for Water Resources, Hydropower: Value To The Nation (Arlington, Virginia: U.S. Army Corps of Engineers, 2009), accessed August 27, 2016, link.This performance far exceeds the 30% to 40% efficiency typical for conventional thermal power plants, and doubles the efficiency of natural gas combined cycles.

Hydroelectric Power is a Function of Height and Volume

\(P = {\eta _{\rm{t}}}\rho Qgh\)

Hydroelectric Power is a Function of Height and Volume

\(P = {\eta _{\rm{t}}}\rho Qgh\)
  • P is power [W]
  • ηt is the dimensionless efficiency of the turbine [approx. 90% or 0.9]
  • ρ is the density of water [1,000 kg/m3]
  • Q is the volumetric flow rate [m3/s]
  • g is the acceleration due to Earth’s gravity [9.8 m/s2]
  • h is the height difference between inlet and outlet [m]

Image Credits: Evgeny Vorobyev/

Hydroelectric Energy

Overall, about 15% of the world’s water is for producing or using energy in one form or another.1International Energy Agency, World Energy Outlook 2012 (Paris: Organization for Economic Cooperation and Development, 2013).While hydroelectric dams appear on the landscape as an obvious use of water for energy, other parts of the energy supply chain also rely on water for a variety of purposes. For example, extractive industries producing fuels such as coal, uranium, oil, and gas use water for flushing fluids out of the ground, controlling dust at mines, or separating out the minerals. In addition, water is an input for energy crops such as corn for ethanol or biomass for fuel pellets. Thermoelectric power plants rely on water for cooling to increase the efficiency of their turbines. In general terms, the use of water improves the energy sector. However, the interdependence of the water and power sectors introduces a major vulnerability to both systems.

The first hydroelectric power plant at Niagara Falls diverted naturally flowing water into the powerhouse without the use of a reservoir.

Built in 1895 in Niagara Falls, New York, the Edward Dean Adams Power Plant was the first large-scale, alternating current electric generating plant in the world. Ten Westinghouse generators provided 37 megawatts of electric power until the plant closed in 1961.

In the United States, the installation of hydroelectric dams accelerated due to economic recovery efforts during the Great Depression and to the military effort of World War II. The Great Depression created the economic motivation for large public works projects, while the war created the demand for electricity. In the 1930s, jobs were scarce, and politicians viewed large water projects as a way to employ the masses while achieving other useful benefits such as providing power and meeting the needs for navigation, commerce, recreation, flood control, and water storage.

This era is when the Hoover Dam (initially named the Boulder Dam) and several other prominent hydroelectric dams—the Shasta and the Grand Coulee—were started. The multi-faceted benefits of dams justify their construction even today. For example, the Sardar Sarovar Dam in India was designed to provide irrigation for one million farmers, drinking water for 29 million people, 1.5 gigawatts (GW) of power, and five thousand new jobs.2“Project At A Glance,” Sardar Sarovar Narmada Nigam Ltd., last modified August 23, 2016, accessed May 24, 2015, link.

Construction crews work on the base of the Grand Coulee Dam in Washington in 1938. The dam is one of dozens of massive water-related projects undertaken by the Public Works Administration during the 1930s.

The simple design of a hydroelectric dam allows for 90% or higher conversion efficiency from the potential energy of the elevated water to electrical energy at the power house.3U.S. Army Engineer Institute for Water Resources, Hydropower: Value To The Nation (Arlington, Virginia: U.S. Army Corps of Engineers, 2009), accessed August 27, 2016, link. This performance far exceeds the typical 30% to 40% efficiency of conventional thermal power plants.

Although hydropower does not burn fuels to generate electricity, hydroelectric dams emit greenhouse gases through their life cycle. Machinery and manufacturing involved in construction have emissions. Furthermore, large reservoirs release significant amounts of methane from the anaerobic decomposition of organic biomatter beneath the water.4Bobby Magill, “Methane Emissions May Swell From Behind Dams,” Scientific American, October 29, 2014, accessed January 1, 2016, link; and Siyue Li and X. X. Lu, “Uncertainties of carbon emission from hydroelectric reservoirs,” Natural Hazards 62 (2012), 1343–1345, accessed August 27, 2016, doi: 10.1007/s11069-012-0127-3. Unfortunately, estimating how much gas bubbles out of the reservoirs is very difficult and rife with uncertainty.

Image Credits: Library of Congress/public domain; U.S. Bureau of Reclamation/public domain.