Connection: Water Supply and Energy Reserves
Water and energy are linked.
in absolute terms, is not in short supply in the world. The world’s
total annual use of commercial energy is on the order of 400 quadrillion
BTUs (Quads), and the sun pours about 6 million Quads of radiant energy
into the earth’s atmosphere each year. What is in short supply is
cheap energy, energy that people can afford to buy. Exactly the same can
be said about water. Water, in absolute terms, is not in short supply in
the world. The earth is a water rich planet, and annual human and animal
consumption is much less than 1% of the world’s total water supply.
What is in short supply is cheap potable water, clean water that people
can afford to buy.
The problem is that 96%, or 317 million cubic miles, is found in the oceans and is saline (35,000 ppm of dissolved salts). Another 7 million cubic miles is tied up in icecaps and glaciers, and 3.1 million in the earth’s atmosphere. Ground water, fresh water lakes, and rivers account for just over 2 million cubic miles of fresh water. The net result is that 99.7% of all the water on earth is not available for human and animal consumption. Of the remaining 0.3%, much is inaccessible due to unreachable locations and depths, and the vast majority of water for human and animal consumption, much less than 1% of the total supply, is stored in ground water.
An important feature of the earth’s supply of fresh water is its non-uniform distribution around the globe. Water, for which there are no substitutes, has always been mankind’s most precious resource. The struggle to control water resources has shaped human political and economic history, and water has been a source of tension wherever water resources are shared by neighboring peoples. Globally, there are 215 international rivers and 300 ground water basins and aquifers shared by two or more countries.
Water-related tensions around the world can have significant implications for U.S. national security. In the Middle East, for example, water is a source of conflict not only between Israel and its Arab neighbors, but also between Egypt and Sudan, and Turkey, Syria, and Iraq. Many have forgotten that the progression towards the 1967 War, whose impact lingers to this day, was triggered by the water dispute between Israel and Syria over control over the Jordan River. Water conflicts add to the instability of a region on which the U.S. depends heavily for oil. Continuation or inflammation of these conflicts could subject U.S. energy supplies to blackmail again, as occurred in the 1970s.
Population growth and economic development are driving a steadily increasing demand for new water supplies, and global demand for water has more than tripled over the past half century. Globally, the largest user of fresh water is agriculture, accounting for roughly three quarters of total use. In Africa this fraction approaches 90%. In the U.S. agriculture accounts for 39% of fresh water use, the same fraction used for cooling thermal power plants.
Future prospects are not encouraging. Global water withdrawal in 2000 is estimated to be 1,000 cubic miles (4,000 km3), about 30% of the world’s total accessible fresh water supply. By 2025 that fraction may reach 70%. Over pumping of ground water by the world’s farmers already exceeds natural replenishment by more than 160 km3, 4% of total withdrawals.
How serious is the situation today? The World Health Organization estimates that, globally, 1.1 billion people lack access to clean water supplies, and that 2.4 billion lack access to basic sanitation. 1,000 m3 is the per capita annual amount of water deemed necessary to satisfy basic human needs. In 1995 166 million people in 18 countries lived below that level. By 2050 potable water availability is projected to fall below that level for 1.7 billion people in 39 countries. Water shortages now plague almost every country in North Africa and the Middle East.
There are significant health impacts of water shortages. Water-borne diseases account for roughly 80% of infections in the developing world. Nearly 4 billion cases of diarrhea occur each year. 200 million people in 74 countries are infected with the parasitic disease schistosomiasis. Intestinal worms infect about 10% of the developing world population. It is estimated that 6 million people are blind from trachoma, and that the population at risk is 500 million.
How much energy is needed to provide water services? As stated earlier, energy is required to lift water from depth in aquifers, pump water through canals and pipes, control water flow and treat waste water, and desalinate brackish or sea water. Globally, commercial energy consumed for delivering water is more than 26 Quads, 7% of total world consumption. Some specific examples follow:
1. Lifting ground water
power needed = (water flow rate)x(water density)x(head)
For example, lifting water from a depth of 100 feet at a flow rate of 20 gallons per minute, and assuming an overall pump efficiency of 50%, requires one horsepower.
2. Pumping water through pipes
power needed = (water flow rate)x (water density)x(H+HL) where H is the lift of water from pump to outflow and HL is the effective head loss from water flow in the pipe.
For example, moving water uphill 100 feet at 3 feet per second through a pipeline that is one mile long and 2 inches in diameter, requires 4.8 horsepower.
3. Energy needed to treat water
Average energy use for water treatment drawn from southern California studies is 652 kWh per acre-foot (AF), where one AF = 325,853 gallons.
4. Energy needed for desalination
There is broad agreement that extensive use of desalination will be required to meet the needs of a growing world population. Energy costs are the principal barrier to its greater use. Worldwide, more than 15,000 units are producing over 32 million cubic meters of fresh water per day. 52% of this capacity is in the Middle East, largely in Saudi Arabia where 30 desalination plants meet 70% of the Kingdom’s present drinking water needs and several new plants are under construction. North America has 16%, Asia 12%, Europe 13%, Africa 4%, Central America 3%, and Australia 0.3%. The two most widely used desalination technologies are reverse osmosis (RO; 44%) and multi-stage flash distillation (MSF; 40%). Energy requirements, exclusive of energy required for pre-treatment, brine disposal and water transport, are: RO: 5,800-12,000 kWh/AF (4.7-5.7 kWh/m3) and MSF: 28,500-33,000 kWh/AF (23-27 kWh/m3).
U.S. water withdrawals in 2000 are shown in Fig. 2. Power plant cooling is the largest user, when total withdrawals (fresh plus saline) are counted. A 500 MWe closed-loop power plant requires 7,000 gallons per minute (10.1 million gallons per day). Of the 195 million gallons per day used in 2000 for cooling thermal power plants, 70% was fresh water, and 30% saline (only about 3% of this water is actually consumed through evaporation). Nationally, power plant cooling and agricultural irrigation each accounted for 39% of fresh water use.
Sustainable withdrawal of fresh water is currently an issue in the U.S. The fast growing demand for clean water, coupled with the need to protect and enhance the environment, has already created shortages in some parts of the U.S. and will make other areas of the U.S. vulnerable to water shortages in the future. For example, California’s allocation of Colorado River water has been reduced because competing urban, agricultural and environmental interests could not agree on a conservation plan. The Ogallala fossil water aquifer in the Central Plains is being depleted by agricultural and urban extraction, with no effective recharge. An increasing number of water disputes are taking place as well in the eastern U.S. - between Virginia and Maryland, Virginia and North Carolina, and among Georgia, Florida and Alabama. Large-scale sea or brackish water desalination is being implemented in Tampa, Florida, and is being planned for sites in California, Texas, Utah and Hawaii.
Competition for fresh water is already limiting energy production. For example, Georgia Power lost a bid to draw water from the Chattahooche River, the Environmental Protection Agency ordered a Massachusetts power plant to reduce its water withdrawals, Idaho has denied water rights requests for several power plants, Duke Power warned Charlotte, NC to reduce its water use, and a Pennsylvania nuclear power plant is planning to use wastewater from coal mines. Other utilities are warning of a power crunch if water availability is reduced.
In response, the Electric Power Research Institute (EPRI), the research and development arm of the private electric utility sector, has initiated a major new research program that will address the connection between fresh water availability and economic sustainability. As a first step, EPRI, which has projected that the world will need 7,000 GW of additional electrical generation capacity by 2050 (today’s total is just over 3,000 GW), undertook a screening study aimed at characterizing the probable magnitude of the quantity of water demanded and supplied, as well as the quality of such water, in the U.S. for the next half century (2000-2050). This screening study, published in 2002, concluded that “…the water budget of the United States in the next 50 years is more uncertain than the currently available predictions suggest,” that “…the cost of insufficient water availability over the next 50 years can be huge,” and that “…water availability can severely constrain electricity growth.”
It is important to emphasize again that we can no longer take water resources for granted if the U.S. is to achieve energy security in the years ahead. This is true of other countries as well, and reflects the strong linkage between water and energy, as well as a growing water security crisis world-wide. Water and energy are also the critical elements of sustainable development, a major goal of U.S. foreign policy. Without access to both, economic growth and job creation cannot take place and poverty cannot be averted.
If our nation is to achieve water and energy security, the linkage between the two must be recognized and acted upon. This will require an enhanced partnership between the federal government, which has primary responsibility for energy security, and the states, where water issues have historically been addressed. The federal government and the states both have much to contribute to such a partnership, which is urgently needed.
Dr. Allan R. Hoffman, Senior Analyst, U.S. Department of Energy (DOE)