Water Supply and Demand

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Water Supply and Demand


Water is essential to human life and to many industries. While by far the largest body of water on Earth is the saltwater of the oceans, freshwater is required for most human activities. However, most freshwater is locked up in glaciers and polar ice caps. Water supplies are drawn mainly from rivers, lakes, and groundwater. The hydrologic or water cycle renews water supplies by moving water from the oceans, as freshwater, to land.

Water consumption varies widely from place to place, but is increasing everywhere as global population rises. Sometimes supply cannot meet local demand, which creates conflict. Climatic factors, such as drought and global warming, water management practices, and over-exploitation place pressure upon water supplies. Diversion of water resources to increase water supplies often has an adverse impact on water quality and the local ecology. Water conservation measures and water management based on sound scientific principles are needed to avert a global water crisis.

Historical Background and cientific Foundations

Around 2.5% of the water on Earth is freshwater and therefore suitable for human use. Of this, only 1% is readily available as a water supply, mainly from lakes, rivers, and groundwater. When rain or snow fall to the ground, as precipitation, some of the water forms surface runoff, moving horizontally under gravity toward the nearest body of water, such as a stream or lake. This surface runoff is the most important source of water supplies. The rest moves vertically into the ground where it fills pores in soil, sand, clay, or rocks known as aquifers. This is known as groundwater, and it is increasingly important as a water supply, although it may require pumping to bring it to the surface.

The availability of freshwater supplies varies between countries. The United Nations keeps an ongoing database that calculates the amount of water available per person in 193 countries. Australia, a dry but large and sparsely populated country, has 6,600,000 gallons per person per year, compared to just over 2,000 gallons per person per year in Kuwait, which is also dry but much smaller. Nearby Bahrain has practically no freshwater of its own and relies on desalination of sea water and imports. The figure for the United States is 2,640,000 gallons per person per year. Many African countries have a lot of water available, such as the Democratic Republic of Congo, which has over 57 million gallons per person per year, while others are short of water, such as Rwanda, which has 161,000 gallons per person per year. Overall, South America, West Central Africa, and South and Southeast Asia have plenty of rainfall, along with Canada and Russia. Egypt, even though it has the River Nile, is relatively water poor, with only 11,000 gallons per person per year.

Most water used for human activities returns to rivers and streams in the form of wastewater. In water calculations, water withdrawal refers to amounts taken from the water supply, some of which will be returned into circulation eventually. Water consumption is the water that is withdrawn and used in such a way that it is not returned to circulation. For instance, some water is lost through leaks, evaporation, or some kind of chemical transformation. Some water that is withdrawn, but not consumed, becomes degraded by pollution or heating so it is no longer suitable for reuse. Water is a renewable resource, through the hydrologic cycle, and the amount of water in the oceans is vast. This fact has led people to take water for granted. But the natural hydrologic cycle is slow and water supplies do not renew themselves overnight. Therefore, it is important to return as much of water withdrawals to the supply as possible by minimizing consumption.

Water use has been increasing as the global population has risen over the last century. It has leveled off in industrialized nations, which tend to have small birth rates, but will continue to increase in developed countries. Global average water withdrawal per person per year is 170,544 gallons. Some countries can meet their population’s demands with ease. Canada, Brazil, and the Democratic Republic of Congo take less than 1% of their water resources for their populations. But Libya and Israel do not have enough surface water to meet demand and are forced to rely on extracting groundwater, which will not be sustainable in the long run.

Water demand comes from the agricultural, industrial, and domestic sectors. Agriculture accounts for the greatest use and consumption of water worldwide. Crop irrigation accounts for two-thirds of water withdrawals and 85% of consumption worldwide. Industry accounts for 20% of water withdrawals worldwide. Industrial water withdrawals vary from up to 70% in countries with a lot of industry, to less than 5% in some less-developed nations. Power production and mining account for the most industrial water use, with water being required for cleaning and cooling processes. Unlike agricultural water, most industrial water can be returned to the water supply, only it will be degraded if it is not treated first.

Domestic water use accounts for around 20% of water withdrawals worldwide. People in wealthy coun-


DESALINATION: Removal of salt from saltwater to produce freshwater.

WATER CONSUMPTION: Use of water in such a way that it cannot be re-used.

WATER STRESS: Inability to provide enough water to meet basic needs.

WATER WITHDRAWAL: Removal of water from a water supply, some of which will later be returned.

tries will use 100 to 200 gallons of water per day, compared to only 7 to 40 gallons a day in developing countries. The major domestic use of water is in toilet flushing. In the United States, the average individual will use 13,000 gallons of water a year in flushing the toilet. Bathing comes next, followed by laundry and dishwashing. Around 6% of domestic water is used for drinking and cooking, and miscellaneous activities like brushing teeth account for the remaining 5%. Since 1960, domestic use of water has grown by about 50% as urban populations have increased.

Impacts and Issues

According to the United Nations, at least one billion people around the world lack access to safe drinking water and 2.6 billion do not have adequate sanitation. Global warming and population growth could exacerbate these shortages in years to come unless water conservation and management practices around the world improve.

At least 45 countries around the world, mainly in Africa or the Middle East, have severe water stress in that they cannot provide enough clean water to meet their citizens’s basic needs. Sometimes a country may have enough water, but it is not clean enough. This is often more of a problem for rural residents than those living in the city. In some developing countries, there is no infrastructure to deliver water so people have to spend many hours fetching water, instead of doing productive work.

Wars have been fought over oil. Water is, arguably, an even more precious resource and scarcities can lead to conflict. Water has not, as yet, been the sole cause of a major war, but is often a factor. For instance, water supplies may be hit as a military target. Most water-centered conflicts have been local. For instance, farmers and traditional herders have clashed over allocations of water in the Ivory Coast, Burkina Faso, and Ghana. There has also been recent conflict between police and farmers in the Hirakud dam area of India over diversion of water to industrial needs. However, water can also promote cooperation, if both sides work together to protect a water resource that spans their countries. Thus, the Indus River Commission continues to function despite ongoing conflict between India and Pakistan.

Primary Source Connection

The Water Sourcebook Series is a project of the Office of Ground Water and Drinking Water (OGWDW). Developed in 2000, the Water Sourcebook Series is the result of a partnership among the EPA Region Four (based in Atlanta, Georgia), the Alabama Department of Environmental Regulation, and Legacy, Inc.

Water Sourcebooks: K-12 is an environmental education program that contains over 300 activities for schoolchildren from kindergarten to twelfth grade—with the reoccurring environmental message, “Use What You Need and Don’t Pollute.” The Water Sourcebook program describes the water management cycle and its effect on all parts of the environment. The curriculum involves science and mathematics, along with subject areas in the social studies, language arts, reading, and other educational areas. The activities involved with the program vary from fact sheets, reference materials, hands-on investigations, and a glossary of terms. Each activity is organized by objectives, materials needed, background information, advance preparation, procedures, and resources.



The value of clean, safe water for individuals, communities, businesses, and industries can’t be measured. Every living thing depends on water. The economy requires it. Water issues should be everyone’s concern, but most people take water quality and availability for granted. After all, clean, safe water is available to most Americans every time they turn on the tap. Water issues do not become a concern until there is a crisis such as a drought or wastewater treatment plant failure. Educating citizens who must make critical water resource decisions in the midst of a crisis rarely results in positive change. Developing awareness, knowledge, and skills for sound water use decisions is very important to young people, for they will soon be making water resource management decisions. Properly equipping them to do so is essential to protect water resources.


The Water Sourcebook educational program is directed specifically toward the in-school population. The program consists of supplemental activity guides targeting kindergarten through high school. Water Sourcebooks are available for primary (K-2), elementary (3-5), middle (6-8), and secondary (9-12) levels. Materials developed in the program are compatible with existing curriculum standards established by State Boards of Education throughout the United States as well as national standards in science, social studies and geography. Concepts included in these standards are taught by using water quality information as the content. The Water Sourcebooks include five chapters—Introduction, Drinking Water and Wastewater Treatment, Groundwater, Surface Water, and Wetlands.


The Water Sourcebooks are developed in three stages. First, classroom teachers are selected to write the activities with assistance of education specialists. Teams of teachers are given the task of developing and writing the activities for each of the five instructional chapters. The second step involves testing activities in the classroom and technical reviews by water experts. From the evaluations provided by the testing teachers and technical reviewers, revisions are made. Finally, editing, and illustrations are complete and the Water Sourcebook is published.


All of the activities include “hands-on” components and are designed to blend with existing curricula in the areas of general sciences, language arts, math, social studies, art, and in some cases, reading or other areas. Each activity details (1) objectives, (2) subjects(s), (3) time, (4) materials, (5) background information, (6) advance preparation, (7) procedure (including activity, follow-up, and extension), and (8) resources. Fact sheets and a glossary section are included at the end of the guide to help equip teachers to deal with concepts and words used in the text which may be unfamiliar.

U.S. Environmental Protection Agency


Primary Source Connection

The following news article reports on how the 2007 California water crisis has resulted in enforced water conservation for both California citizens and businesses. Tim Quinn, executive director of the Association of California Water Agencies, explains the difficulty of California’s water issue as, “the clash between the environment, the California economy, and the population, which is pouring in at more than 600,000 per year.” Water conservation measures are also affecting the economy of the state, especially the farmers and manufacturers, and water supply measures are sometimes at odds with environmentalists.


California farmers, who produce half the nation’s fruits and vegetables, say they will idle fields and cut back on planting lettuce, cotton, rice, and more.

Silicon Valley computer-chip makers and other industrial/commercial users say they will rethink manufacturing processes that use water, or dramatically raise the price of products they sell.

Cities from Sacramento to San Diego say drought-era practices of rationed water—low-use toilets and washers, designated water days for lawns and cars—are back, including stiff fines for those who don’t follow the rules.

After 35 years of hemming and hawing over how to fix the largest estuary in the Western Hemisphere—the sprawl of canals, levees, and flood plains that join the Golden State’s two river systems—the state has been told by a federal judge that business-as-usual is now illegal.

A new ruling to stop pumping up to 37 percent of the water that flows through the delta to protect endangered fish species has sent shock waves of concern into the three main sectors that have long competed for it: cities, farms, environment.

The estuary provides water to 23 million Californians and about 5 million acres of farmland. Overused and under maintained for years, the delta and its water are at the heart of the state’s economic vitality, its wildlife habitat, shipping, transportation, drinking water, and recreation.

“In the water business we are facing the biggest challenges here in over half a century… there is no way any knowledgeable person could contest that,” says Tim Quinn, executive director of the Association of California Water Agencies, which represents more than 450 of the state’s water agencies that provide water to 95 percent of the state’s farms and cities. “The state has had some success in better managing this problem for the last decade, but we have hid ourselves from the biggest issue… and Mother Nature is telling us there is no more hiding.”

The biggest issue, say Mr. Quinn and others, is the clash between the environment, the California economy, and the population, which is pouring in at more than 600,000 per year.

In recent years, the use of water in the delta has been crippled as a result of drought as well as age, with deteriorating levees that are vulnerable to flood, earthquake, and subsidence. It was environmental groups who most recently challenged water use. The ruling by U.S. District Court Judge Oliver Wanger in Fresno Aug. 31came after a suit against state and federal water officials by the Natural Resources Defense Council (NRDC) and three other environmental groups.

The agricultural community in the Central Valley appears to be the most worried about the consequences of the judge’s action.

Stephen Patricio, chairman of the board of directors for the Western Growers Association and a 30-year farmer of 2,000 acres of cantaloupe near Firebaugh, Calif., says the impact of a 30 percent or more reduction of water to his region will have a domino effect on other jobs.

He expects his $6 million payroll, employing about 600 people during the harvest, will drop to about $1.5 million this year and force him to cut 400 jobs. Those losses will contribute to another 2,400 layoffs in related industries: truck drivers, tractor operators, seed operations, warehousing, repair, and fuel, he says.

The announcement is already having an effect on the loans farmers receive to operate their farms during 2008.

“Ninety percent of these farms need to be financed, and lenders have made it very clear that without a water plan, there is no money for 2008 crops,” Mr. Patricio says.

Eighty percent of the water in California moves from above the delta to farms and communities in the south of it via pumps. The environmental groups said that current use of water pumping through the delta endangered several species of fish, including two kinds of smelt (long fin and delta), steel head, green sturgeon, winter and spring salmon, and split tail.

“ThThis ruling was essentially an agreement that we need to protect habitat in the delta more than we have been, and what state and federal agencies have been doing is likely to drive the smelt to extinction,” says Barry Nelson of the NRDC. “For all the serious concern about how the state is now going to meet its water needs, no one is saying that the court got it wrong. Everyone has known for a long time that this was coming.”

Water agencies, farmers, and scientists agree, saying the ruling will force a much-needed opportunity to fine-tune the use of water to avoid waste.

“This alarm as been sounding about the delta for 30 years, and we’ve been pushing the snooze alarm,” says Peter Gleick, president of the Pacific Institute, a nonprofit think tank in Oakland, Calif. “This may lead to some of the first discussions ever on how we manage growth in the state, how people live, how much we waste, and what crops we farm.”

He notes that farming just three common crops—rice, cotton, and alfalfa—as well as irrigated pastures for cows use about half of the agricultural sector’s allotment but earn a fraction of agricultural income. “We can continue to have a healthy economy with less water, but there has been no demand to do that yet,” he says. “This ruling may drive us to do things we ought to be doing anyway.”

Anticipating the reduced water spigot from the delta as of January 2008, water agencies north of it are telling their clients to cut back on water use. They are already spending money in new ad campaigns to remind users to cut back or face the possibility of mandatory laws with fines.

“We are spending millions to get the conservation message out that we need to conserve as if we are in a crunch,” says Jeff Kightlinger, of the Metropolitan Water District of Southern California, which serves agencies and 18 million residents in six counties. He says the new rationing will affect 2 of every 3 Californians.

“Farmers across the state know this will be very tough and not pleasant,” says Dave Kranz, spokesman for the California Farm Bureau Federation. “To the extent that ou take farmland out of production for whatever rea-on, it increases another problem, which is providing enough American-grown food to serve the US population as well as demand from other countries.”

Solutions are now in the works. A commission appointed by Gov. Arnold Schwarzenegger is planning to make recommendations next month, including ideas for dams and more storage capacity.

State Senate President pro tem Don Perata (D) is pushing two measures. One provides $200 million for immediate safeguards of freshwater flows from north to south. The second is a $5 billion bond that includes $2 billion to fix the water supply, improve flood protection, and boost fisheries in the delta, and $2 billion for water storage projects such as dams.

Daniel B. Wood


See Also Groundwater; Surface Water; Water Conservation; Water Resources



Cunningham, W.P., and A. Cunningham. Environmental Science: A Global Concern. New York: McGraw-Hill International Edition, 2008.

Kaufmann, R., and C. Cleveland. Environmental Science. New York: McGraw-Hill International Edition, 2008.

Web Sites

Green Facts: Facts on Health and Environment. “Scientific Facts on Water Resources.” http://www.greenfacts.org/en/water-resources/index.htm#2 (accessed July 15, 2008).

Pacific Institute: The World’s Water. “Water and Conflict.” February 2008. http://www.worldwater.org/conflict.html (accessed March 25, 2008).

Susan Aldridge