This article discusses increasing use of energy water due to increasing unavailability of fresh water. There has been an increasing demand for energy and water even faster than population increase, driven by economic growth on top of the population growth. The increased energy intensity of water has several different components, including stricter water/wastewater treatment standards, deeper aquifer production, long-haul pipelines, and desalination. Each of those elements is more energy intensive than conventional piped water today, and seems to be a more common option moving forward. Rapid desalination growth is also occurring in China, where booming industrial activity is straining water supplies that serve the world’s largest population. While trading energy for water makes a lot of sense in places such as the Middle East or Libya, where there is an abundance of energy and a scarcity of freshwater, that trade-off is not obviously an excellent value in places such as the United Kingdom or the United States, where other cost-effective options such as water conservation, graywater capture, and water reuse might be available.
The word “tantalize” has its roots in a water-based legend. The Greek gods punished Tantalus, a son of Zeus, by giving him a great thirst and forcing him to stand in a pool of water that always recedes as he leans down to take a drink.
Such a myth feels like a fitting parable for humankind's relationship with abundant water resources that seem to be forever beyond our reach. In fact, it is this inconvenience that drives much of our energy investments for water: we spend significant sums of energy moving, treating, or storing water so that it is available in the form, location, and time we want it. While those energy investments overcome the limits of water's tantalizingly distant location, billions of people still remain without clean, accessible water.
What's more, demand for energy and water has been growing faster than population, driven by economic growth on top of the population growth. Affluent people eat more meat and consume more electricity—two activities that use water. With many water withdrawals coming from nonrenewable resources, the trends for greater consumption will trigger water shortages unless something changes.
Austin's Water Treatment Plant 4, completed in 2014, is capable of treating 50 million gallons a day with room to expand to 300 mgd.
By 2005, at least half of Saudi Arabia's fossil (nonrenewable) water reserves had been consumed in the previous two decades. Significant declines have also been observed in the Ogallala Aquifer under the Great Plains of the United States, spanning eight states from South Dakota to Texas. Water tables in Texas have lowered by as much as 234 feet, while the average drop across the entire aquifer was 14 feet. Storage of water fell from 3.2 billion to 2.9 billion acre-feet.
Overall, water availability is declining globally. Available water dropped from 17,000 cubic meters per person in 1950 to 7,000 cubic meters per person in 2000. Water stress occurs between 1,000 and 1,700 cubic meters, and a water crisis occurs at less than 1,000 cubic meters. Notably, counties such as Qatar, Libya, and Israel are well below 400 cubic meters per person, and even the “green and pleasant” United Kingdom only has 1,222 cubic meters.
All of these datasets point toward a conclusion that water stress is increasing. High-profile research published in Nature has concluded that nearly 80 percent of the global population endures high levels of threat to water security.
To compensate for the decline in water availability, we are moving toward more energy-intensive water. This relationship is just one aspect of the energy-water nexus: the dependency of water availability on energy inputs, and the dependency of power generation on available water. The increased energy intensity of water has several different components, including stricter water/wastewater treatment standards, deeper aquifer production, long-haul pipelines, and desalination. Each of those elements is more energy intensive than conventional piped water today, and seems to be a more common option moving forward.
As societies become wealthier, their concerns shift from focusing on economic growth to protecting the environment. Protecting drinking water quality and preserving the ecosystem from the discharge of water treatment plants are two important pieces of that trend.
But water and wastewater treatment require nontrivial amounts of energy, and advanced treatment methods to meet stricter standards are more energy intensive than treatment for lower standards. For example, advanced treatment systems for wastewater with nitrification require about twice as much energy as trickling filter systems. As we tighten the standards for water and wastewater treatment, we are essentially edging toward increases in energy consumption. While new treatment technologies and methods become more efficient over time after their initial implementation, the standards tighten in parallel. How these balance out is unclear.
At the same time, the water coming into water and wastewater treatment plants is getting more polluted with time. As population grows, there are more discharges into the waterways. Those discharges contain constituents that weren’t always there in such high concentrations. For example, there have been growing concerns about pharmaceuticals (including birth-control pills and pain pills) in sewage streams, which are difficult for wastewater treatment plants to remove. Doing so requires new equipment and ongoing investments of energy.
In an ironic example of the energy-water nexus, some of our energy choices create water quality impacts that require additional energy to treat. For example, increased biofuels production from Midwest corn is expected to cause additional runoff of nitrogen-based fertilizers and other pollution that will require more energy to remove.
Also, the wastewater streams from hydraulic fracturing of shales to produce oil and gas contain much higher levels of total dissolved solids than most wastewater treatment plants can handle. That means more energy has to be spent in one of several ways: on trucking that wastewater to disposal sites or specialized industrial wastewater treatment facilities that might be far away (something that happens rarely), for on-site treatment to recycle and reuse the water in subsequent wells, or on new equipment at the wastewater treatment plant to treat those streams. Even that new equipment is sure to require energy.
We are also contemplating moving water farther from its source to the end user. Long-haul pipelines and inter-basin transfer, which is moving water from one river basin to another, are common proposals to solve the crisis of declining local water supplies. While the idea of aqueducts has been around for thousands of years, the scale, length, and volumes of water that are moved are growing.
Some of the classic water transfer systems include the State Water Project in California, which is the state's largest electricity user because it must pump the water over mountains. (It also captures a lot of energy when the water flows back downhill through inline hydroelectric turbines coupled with chutes.) The Hawaiian island of Maui has an incredible series of hand-cut water channels that circle its two volcanoes, moving water miles from the wet portion of the island—one of the wettest places in the United States—to the dry inland plains where farming occurs. This system operates by gravity, and also generates electricity along the way.
Moving forward, as water tables fall and surface sources dry up, municipalities are more likely to consider the cost of expensive and far-flung watergathering systems that pull water to a city from deeper in the ground or farther away. These long-haul systems will generally not be gravity-fed and will require a lot of energy. Plus, they will impact the ecosystem as water from one basin is moved to another, both in terms of loss of water in one watershed and the potential for invasive species in the other.
Perhaps the most ambitious water project in the world is the South-North Transfer Project in China (also known as the South-North Water Diversion Project, or SNWD). The scale, scope, and ambition of the project is reminiscent of U.S. water planners who have dreamed for decades of diverting the Yukon River in Alaska or the Missouri River in the Great Plains to the American Southwest, so that the deserts would bloom with flowers and fruit trees. This project essentially aims to move major southern rivers—the Yangtze and Han—across the country to the Yellow and Hai Rivers. The industrialized north is relatively water poor, whereas the southern part of China is relatively water rich. The total estimated flow for the Chinese endeavor is projected to divert 44.8 billion cubic meters per year from the south more than a thousand miles to the north, at a total cost estimated to be $62 billion.
Not to be left out, India is also building its own long-haul water pipeline. And joining the pack, Texas is, too. For example, in Texas, a 240-mile pipeline is being built to bring 370,000 cubic meters per day of water from Lake Palestine to the Dallas-Fort Worth Metroplex. The total capital cost for the construction is estimated to be $888 million, or $3.7 million per mile of pipeline. The annual electricity consumption is expected to be $11.3 million, or $0.71 per cubic meter.
In addition, there is a water pipeline that oil and gas tycoon T. Boone Pickens proposed in early 2008 with the expectation that water would be the new oil. The pipeline would move water from Roberts County in the panhandle of Texas toward the Dallas-Fort Worth Metroplex. This project was controversial for a variety of reasons, one of which is that the water rights Pickens holds are for fossil water in the Ogallala aquifer, which can take millions of years to recharge. In Dallas, one of the likely applications for that fossil water would be for sustaining lawns.
While some energy would be used for pumping the water out of the aquifer, once it is at the surface, the water would mostly use gravity for its downhill trip to Dallas. Ultimately the deal was scuttled because of the $3 billion price tag for the pipeline. Instead, Pickens sold the water rights to thirsty local cities.
Another of the key trends to watch is how many municipalities are turning to desalination as a solution for water supply issues. In 2013, over 17,000 desalination plants were already installed worldwide, providing approximately 21 billion gallons per day (67 million cubic meters per day) of freshwater. With a blistering pace of growth, that capacity is projected to keep expanding quickly. More than three-fourths of new capacity will be for desalinating seawater, with the rest from brackish groundwater or salty rivers.
While thermal desalination (using heat) represents about 25 percent of the installed capacity by 2010, it represents a shrinking share of new installations as builders seek the less energy intensive reverse osmosis membrane-based system. Even with the lower-energy approach, desalination is still an order of magnitude more energy-intensive than traditional freshwater treatment and distribution. Desalination is capital intensive, too: The annual global desalination market exceeds $10 billion.
Growth in desalination is particularly rapid in energy-rich, water-poor parts of the world, such as the Middle East, northern Africa, and Australia. After a severe drought that lasted several years, water-strapped Israel famously turned to the sea for its water, rapidly building a handful of desalination plants to produce about 200 billion gallons of freshwater annually by desalting water from the Mediterranean.
Rapid desalination growth is also occurring in China, where booming industrial activity is straining water supplies that serve the world's largest population. It is also popping up in locations such as London, where a new desalination plant was very controversial and became a big part of several mayoral campaigns.
Despite its relative water wealth, the United States is the world's second-largest market for desalination, trailing only Saudi Arabia. This phenomenon is partly the result of the unequal distribution of water resources across the United States. And, as a wealthy country, the water consumption per capi-ta is quite high and the money to finance large-scale infrastructure projects is available. Projects are un-der consideration for seawater reverse osmosis in coastal states such as California, Texas, and Florida. And projects are under development to serve inland communities that sit atop large brackish aquifers, as in Texas, Arizona, and New Mexico.
The two most energy-intensive options—desalination and long-haul transfer—can also be combined to create an even larger energy requirement for water. Natural water flows occur by gravity, but for seawater desalination, the opposite is true. By definition, coastal waters are at sea level, so moving the water inland requires pumping water uphill. One such desalination project under development in the United States is a coastal facility along the Gulf of Mexico that is designed to provide freshwater for San Antonio, Texas. That means the water would be moved nearly 150 miles inland, increasing in elevation nearly 775 feet.
While trading energy for water makes a lot of sense in places like the Middle East or Libya, where there is an abundance of energy and a scarcity of freshwater, that tradeoff is not obviously a good value in places like the United Kingdom or the United States, where other cost-effective options such as water conservation, graywater capture, and water reuse might be available.
In the end, the most important innovation we need is a new way of thinking about energy and water so that we make better decisions about those precious resources: holistic thinking that recognizes these resources as interconnected, and a systems-level approach that acknowledges how one change in one state to a water system can impact an energy system five states away.
Most important, we need long-range thinking because our energy and water decisions last decades to centuries, so it's imperative that we get them right.