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Water Issues - Water Availability

percent irrigation supply stream

Water must be considered as a finite resource that has limits and boundaries to its availability and suitability for use.

—Wayne B. Solley, Robert R. Pierce, and Howard A. Perlman in Estimated Use of Water in the United States in 1995, U.S. Geological Survey, 1998

Although water covers nearly three-fourths of the planet, the vast majority of it is saline (water that contains at least 1000 milligrams of salt per liter of water). It is too salty to drink or nourish crops and too corrosive for many industrial processes. No cheap and effective method for desalinating large amounts of ocean water has yet to be discovered. This makes freshwater an extremely valuable commodity. While the overall water supply on Earth is enormous, freshwater is not often in the right place at the right time in the right amount to serve all of the competing needs.

Throughout history civilizations originated and declined based on the availability of water. Water supply in the United States is becoming a serious problem. The days of an unlimited bounty of water are over.

Overall Water Use in 2000

Water use in the United States is monitored and reported by the U.S. Geological Survey (USGS) in its Estimated Use of Water in the United States, published at five-year intervals since 1950. The latest report available was published in 2004 and includes data through 2000.

For reporting purposes, water use in the United States is classified as in-stream or off-stream. In-stream use means the water is used at its source, usually a river or stream, for example, for the production of hydroelectric power at a dam. Off-stream use means the water is conveyed away from its source, although it may be returned later.


The 2000 USGS report found that an estimated 408 billion gallons of water per day were withdrawn from surface and groundwater sources for offstream use in 2000. (See Table 6.1.) Of this total, 47.8 percent was withdrawn for generation of thermoelectric FIGURE 6.1
The water cycle
power, approximately 33.6 percent was used for irrigation, and about 10.6 percent went to public water supply. Together these three uses accounted for about 92 percent of the total water used.

Minor uses included miscellaneous industrial (including commercial and mining), livestock and aquaculture, and self-supplied domestic (from private wells). Complete data were not available for all minor uses in 2000.

Together only three states—California, Texas, and Florida—accounted for 25 percent of all off-stream water withdrawals in 2000. Irrigation and thermoelectric power generation were the primary users in these states.

In-stream water use for the generation of hydroelectric power at dams was not reported by USGS for 2000 but totaled 3.16 trillion gallons of water per day in the 1995 report. According to the U.S. Department of Energy, there are approximately 2,000 dams with hydroelectric generating capacity in the United States. Most are located in the Pacific Coast states of California, Oregon, and Washington. In-stream water usage is highest at dams along the

Trends in estimated water use, 1950–2000

Year Percentage change
11950 21955 31960 41965 41970 31975 31980 31985 31990 31995 32000 1995–2000
Population, in millions 150.7 164.0 179.3 193.8 205.9 216.4 229.6 242.4 252.3 267.1 285.3 +7
Offstream use:
Total withdrawals 180 240 270 310 370 420 440 399 408 402 408 2
Public supply 14 17 21 24 27 29 34 36.5 38.5 40.2 43.3 8
Rural domestic and livestock:
Self-supplied domestic 2.1 2.1 2.0 2.3 2.6 2.8 3.4 3.32 3.39 3.39 3.59 6
Livestock and aquaculture 1.5 1.5 1.6 1.7 1.9 2.1 2.2 5 4.47 4.50 5.49 6
Irrigation 89 110 110 120 130 140 150 137 137 134 137 2
Thermoelectric power use 40 72 100 130 170 200 210 187 195 190 195 3
Other industrial use 37 39 38 46 47 45 45 30.5 29.9 29.1 7
Source of water:
Fresh 34 47 50 60 68 82 83 73.2 79.4 76.4 83.3 9
Saline 8 0.6 0.4 0.5 1.0 1.0 0.9 0.65 1.22 1.11 1.26 14
Fresh 140 180 190 210 250 260 290 265 259 264 262 1
Saline 10 18 31 43 53 69 71 59.6 68.2 59.7 61 2
148 states and District of Columbia, and Hawaii
248 states and District of Columbia
350 states and District of Columbia, Puerto Rico, and U.S. Virgin Islands
450 states and District of Columbia, and Puerto Rico
5From 1985 to present this category includes water use for fish farms
6Data not available for all states; partial total was 5.46
7Commercial use not available; industrial and mining use totaled 23.2
8Data not available
SOURCE: Susan S. Hutson, Nancy L. Barber, Joan F. Kenny, Kristin S. Linsey, Deborah S. Lumia, and Molly A. Maupin, "Table 14. Trends in Estimated Water Use in the United States, 1950–2000," in Estimated Use of Water in the United States in 2000, (Circular 1268), U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, April 2004 [Online] [accessed May 4, 2004]

Columbia River in the Pacific Northwest and along the Niagara and St. Lawrence River systems in New York.


In 2000 freshwater accounted for 345.3 billion gallons per day or 85 percent of total offstream water withdrawals. Freshwater is used exclusively for public water supply, domestic self-supply (private wells), irrigation, livestock watering, and aquaculture. It is also an important source for thermoelectric power plants, industry, and mining. Most freshwater is obtained from surface water sources (rivers and lakes), as shown in Figure 6.2.

Irrigation and thermoelectric power plants are the largest users of off-stream freshwater, each accounting for approximately 40 percent of its use. However, the vast majority (around 97 percent) of the water withdrawn for thermoelectric power generation is used for cooling purposes and then discharged, meaning the actual amount of water consumed is much smaller. The United States Department of Agriculture (USDA) estimates that approximately 60 percent of the water withdrawn for irrigation purposes is consumed. This makes irrigation the largest consumer of freshwater.

Nearly all (98 percent) of the saline water used in 2000 came from surface water sources. Far less saline water than freshwater was used in 2000. Only 15 percent of all water used was saline. Thermoelectric power plants are the largest user of saline water. They accounted for 96 percent of all saline water use in 2000. Again, most of this water was used and returned to the environment. Industry and mining each accounted for 2 percent of saline water use. Saline water is unsuitable for drinking and other domestic purposes, irrigation, aquaculture, or livestock watering.

In 2000 California and Texas accounted for 18 percent of all off-stream freshwater use. California and Florida accounted for 40 percent of all saline water use.


The USGS estimates that 79 percent of all off-stream water used in 2000 was from surface water. The other 21 percent was from groundwater. Figure 6.3 shows the breakdown of surface water users. Thermoelectric power plants, irrigation, and public water supply were the primary users. Figure 6.4 shows the user breakdown for ground water. Irrigation and public supply were the primary users.

Water Use Trends (1950–2000)

According to the USGS, total off-stream water withdrawals in the United States climbed steadily from 1950 FIGURE 6.2
Trends in population and use of ground water and surface water, 1950–2000
to 1980, declined through 1985 and have remained relatively stable since then. (See Figure 6.5.)

Experts believe the general increase in water use from 1950 to 1980 and the decrease from 1980 to 2000 can be attributed to several factors:

  • The expansion of irrigation systems and increases in energy development from 1950 to 1980 increased the demand for water.
  • In some western areas the application of water directly to the roots of plants by center-pivot irrigation systems has replaced sprayer arms that project the water into the air, where much is lost to wind and evaporation.
  • Higher energy prices in the 1970s and a decrease in groundwater levels in some areas increased the cost of irrigation water.
  • A downturn in the farm economy reduced demands for irrigation water.
  • New industrial technologies requiring less water, as well as improved efficiency, increased water recycling, higher energy prices, and changes in the law to reduce pollution decreased the demand for water.
  • Increased awareness by the general public and active conservation programs reduced the demand for water.

Table 6.1 shows trends in U.S. population and offstream water withdrawals for the period 1950–2000. The population increased by 89 percent over this time period, while water withdrawn increased by 127 percent. In 1950 the per capita (per person) off-stream water withdrawal was around 1,200 gallons per day. This value climbed steadily over the years, reaching a peak in 1975 of 1,940 gallons per day per person. Per capita use has since declined and was at 1,430 gallons per day per person in 2000.

Historically freshwater has accounted for 85–95 percent of all water used. The percentage was at the high end during the 1950s and has gradually decreased, leveling off around 85 percent from 1980 through 2000. The nation's saline water withdrawals have consistently been 98–99 percent from surface water sources.

Although in-stream water use for hydroelectric power is not covered in the 2000 USGS report, the 1995 report notes that in-stream withdrawals declined 4 percent between 1990 and 1995, from 3,290 to 3,160 billion gallons per day.

The Freshwater Supply

Most great civilizations began and flourished on the banks of lakes and rivers. Throughout human history societies have depended on these surface water resources for food, drinking water, transportation, commerce, power, and recreation.

The withdrawal of surface water varies greatly depending on its location. In New England, for example, FIGURE 6.3
Estimated use of surface water, 2000
where rainfall is plentiful, less than 1 percent of the annual renewable water supply is used. In contrast, almost the entire annual supply is consumed in the area of the arid Colorado River Basin and the Rio Grande Valley.


Dams have changed the natural water cycle. The huge dams built in the United States just before and after World War II substantially changed the natural flow of rivers. By reducing the amount of water available downstream and slowing stream flow, a dam not only affects a river but the river's entire ecological system.

Some 100,000 dams regulate America's rivers and creeks. Nationwide, reservoirs encompass an area equivalent to New Hampshire and Vermont combined. Of all the major rivers (more than 600 miles in length) in the 48 contiguous states, only the Yellowstone River still flows freely. America is second only to China in the use of dams. Worldwide, dams collectively store 15 percent of Earth's annual renewable water supply. Globally, water demand has more than tripled since the mid-twentieth century, and the rising demand has been met by building ever more and larger water supply projects.

Being a world leader in dams was a point of pride for the United States during the golden age of dam building, a FIGURE 6.4
Estimated use of ground water, 2000
50-year flurry of architectural innovation that began with the construction of the massive Hoover Dam on the lower Colorado River in the 1930s and ended in approximately 1980. In the early years the Army Corps of Engineers built most dams for flood control; later projects served narrower interests, such as developers who wanted flood-plain land.

Dams epitomized progress, Yankee ingenuity, and humankind's mastery of nature. However, the very success of the dam-building endeavor accounted, in part, for its decline: by 1980 nearly all the nation's good sites—and many dubious ones—had been dammed. There were few appropriate places left in the United States to build a major dam.

Three other factors, however, accounted for most of the decline: public resistance to the enormous costs; a growing belief that politicians were foolishly spending taxpayers' money on "pork barrel" (local) projects, including dams; and a developing public awareness of the profound environmental degradation that dams can cause.


Dams provide a source of energy generation; flood control; irrigation; FIGURE 6.5
Trends in water use by category, 1950–2000
recreation for pleasure boaters, skiers, and anglers; and locks for the passage of barges and commercial shipping vessels. But dams alter rivers as well as the land abutting them, the water bodies they join, and the aquatic life they contain. All this results in profound changes in water systems and the ecosystems they support.

Many regions have fallen into a zero-sum game in which increasing the water supply to one user means taking it away from another. More water devoted to human activities means serious and potentially irreversible harm to natural systems. Many experts believe that the manipulation of river systems is wreaking havoc on the aquatic environment and its biological diversity. Hundreds of species or subspecies of fish are threatened or endangered because of habitat destruction. When rivers are dammed and water flow is stopped or reduced, wetlands dry up, species die, and nutrient loads carried by rivers into the sea are altered, with many negative consequences. Some rivers, including the large Colorado River, no longer reach the sea at all except in years of very high precipitation.

Concern for damage to the environment led Congress to pass the Grand Canyon Protection Act of 1992. The act directed the secretary of state to protect the Grand Canyon basin and its life forms and to monitor the effects of damming the Colorado River. Out of concern for any damage possibly being done to the canyon, for a two-week period in 1996 the Bureau of Reclamation conducted a controlled flood of the canyon by releasing water from the Glen Canyon Dam (up-canyon). The flooding created dozens of new beaches in the Grand Canyon, cleared out many harmful nonnative species, and invigorated fish habitats. The Environmental Protection Agency (EPA) reported that the release of water was significant in that "it was the first time in [U.S.] history that the economic agenda of a large water project was put aside purely for the good of the ecological resources downstream."


Deforestation and over-grazing have destroyed thousands of acres of vegetation that play a vital role in controlling erosion. Erosion leads to soil runoff into rivers and streams, causing disruption of stream flow. Destruction of vegetation reduces the amount of water released into the atmosphere by transpiration and less water in the atmosphere can mean less rainfall, which can, in turn, lead to desertification (transformation to desert) of once-fertile regions.

The most severe form of land degradation—desertification—is most acute in arid regions. Where land degradation has begun, the hydrologic cycle is disrupted, leaving water tables depleted and causing the sinking and drying of the land. Although desertification was long thought to be the result of droughts, there is much more involved in the process of degradation and desertification of grazing land, including:

  • vegetation loss
  • water erosion
  • wind erosion
  • salinization
  • compaction of the land by machinery
  • accumulation of toxic substances such as lead, chromium, pesticides, and industrial waste

A few hundred million years ago oceanic waters were still fresh enough to drink. It is the Earth that contains the mineral salts that one tastes in seawater. These salts are leached from soil and rock by runoff water. The runoff concentrations in rivers end up in the oceans or in salt lakes such as Mono Lake in California and the Great Salt Lake in Utah. These lakes are seven times saltier than the sea. Once in these bodies of water the salts have nowhere to go. Continuous runoff and evaporation of water leaves increasingly higher concentrations of salt, gradually causing the oceans or lakes to grow saltier. What is changing, however, is the drastic increase in concentrations of salt in the nation's rivers and on some of its prime agricultural land.


Groundwater is water that fills pores or cracks in subsurface rocks. When rain falls or snow melts on the Earth's surface, water may run off into lower land areas or lakes and streams. Some is caught and diverted for human use. What is left is absorbed into the soil where it can be used by vegetation; seeps into deeper layers of soil and rock; or evaporates back into the atmosphere. (See Figure 6.6.)

Below the topsoil is an area called the unsaturated zone where, in times of adequate rainfall, the small spaces between rocks and grains of soil contain at least some water, while the larger spaces contain mostly air. After a major rain the zone may become saturated—that is, all the open spaces fill with water. During a drought, the area may become drained and almost completely dry.

With excessive rainfall, water will drain through the unsaturated zone (which has now absorbed as much water as it can hold) to the saturated zone. The saturated zone is always full of water—all the spaces between soil and rocks, and the rocks themselves, contain water. In the saturated zone water is under higher-than-atmospheric pressure. Thus, when a well is dug into the saturated zone, water flows from the area of higher pressure (in the FIGURE 6.6
Groundwater in the hydrologic cycle
ground) to the area of lower pressure (in the hollow well), and the well fills with water to the level of the existing water table (the level of groundwater). A well dug just into the unsaturated zone will not fill with water because the water in the unsaturated zone is at atmospheric pressure.

The water table is the level at which the unsaturated zone and the saturated zone meet. The water table is not fixed but may rise or fall, depending on water availability. In areas where the climate is fairly consistent, the level of the water table may vary little; in areas subject to extreme flooding and drought it may rise and fall substantially.

An aquifer is an underground formation that contains enough water to yield significant amounts when a well is sunk. The formation of an aquifer is actually a path of porous or permeable material through which substantial quantities of water flow relatively easily. The word "aquifer" comes from the Latin aqua (water) and ferre (to bear or carry). An aquifer can be a layer of gravel or sand, a layer of sandstone or cavernous limestone, a rubble zone between lava flows, or even a large body of massive rock, such as fractured granite.

Aquifers vary from a few feet thick to tens or hundreds of feet thick. They can be located just below the Earth's surface or thousands of feet beneath it, and one aquifer may be only a part of a large system of aquifers that feed into one another. They can cover a few acres of land or many thousands of square miles. Because runoff water can easily seep down to the water table, aquifers are susceptible to contamination.

Modern technological developments allow massive quantities of water to be pumped out of the ground. When large amounts of water are removed from the ground, underground aquifers can become depleted much more quickly than they can naturally be replenished. On almost every continent, many major aquifers are being drained faster than their natural rate of recharge. Depletion is most severe in India, China, the United States, North Africa, and the Middle East. In some areas this has led to the subsidence, or sinking, of the ground above major aquifers. Farmers in California's San Joaquin Valley began tapping the area's aquifer in the late nineteenth century. Since that time dehydration of the aquifer has caused the soil to subside by as much as 29 feet, cracking foundations, canals, and roadways. Removal of groundwater also disturbs the natural filtering process that occurs as water travels through rocks and sand.

Focus on Irrigation

In 2000 irrigation accounted for 40 percent of all the freshwater withdrawn that year. It was by far the largest single user of groundwater and second-highest user of surface water (behind thermoelectric power plants). Because irrigation consumes more withdrawn water than do thermoelectric power plants, irrigation is actually the largest consumer of both surface water and groundwater.

Large-scale irrigation is concentrated in the Midwestern farm belt, southern Florida, the fertile valleys of California, and along the Mississippi River. According to the U.S. Department of Agriculture, more than 50 million acres were irrigated in 1997, primarily in western states. Figure 6.7 shows total irrigation withdrawals by state. California and Idaho withdrew 15–30 billion gallons of water per day for irrigation during 2000. Many states west of the Mississippi River withdrew at least 1 billion gallons per day for irrigation.

A Water Crisis Looming in the West?

In much of the American West, millions of acres of profitable land overlie a shallow and impermeable clay layer, the residual bottom of an ancient sea, that is sometimes only a few feet below the Earth's surface. During the irrigation season, temperatures in much of the region fluctuate between 90 and 110 degrees Fahrenheit. The good water evaporates and polluted and saline water seep downward. Very little of this water seeps through the clay. As the water supplies are replenished with rainfall, the water table—now high in concentrations of salts and pollutants—rises back up through the root zone (the area containing plant roots), soaking the land and killing crops. (In general, high salt concentrations obstruct germination and impede the absorption of nutrients by plants.)

Several thousand acres in the West have already gone out of production and salt covers the ground like a dusting of snow; not even weeds can grow there. In the coming decades, as irrigation continues, that acreage is expected to increase dramatically. It is this process rather than drought that is believed to have resulted in the decline of ancient civilizations such as Mesopotamia, Assyria, and Carthage.


Many of the fastest growing states are in the West. The U.S. Census Bureau expects population growth in California, Nevada, Arizona, and New Mexico to be in excess of 50 percent between 1995 and 2025. All of the states neighboring them are expected to grow by 31–50 percent.

This population growth in the West is expected to put enormous pressure on natural resources, including water, and to force huge changes in water consumption practices and prices.


The natural hydrologic cycle, already under pressure by such human uses as irrigation, is also under strain from years of drought. Although there is no set definition of what constitutes a drought, it is commonly used to describe a period of at least several months in which precipitation is significantly less than that normally expected based on historical records.

According to the Climate Prediction Center of the National Weather Service, drought affected approximately 30 percent of the country in the spring of 2004. Persistent drought was forecast for the entire states of Nevada, Utah, Arizona, Wyoming and parts of California, Oregon, Idaho, Montana, Colorado, and New Mexico. During the 1930s the so-called "Dust Bowl" drought engulfed up to 70 percent of the country.

WATER 2025.

Although drought is a serious concern in the West, it is not the only worry related to water resources. In 2001 the Bush administration asked the Bureau of Reclamation to assess existing water supplies across the west and identify areas likely to experience severe water shortages within the coming decades. The result was a comprehensive report published in May 2003 titled Water 2025: Preventing Crises and Conflict in the West.

The report reviews the factors aggravating the water problems in the West, mainly booming population growth in the most arid regions, aging and poorly maintained water supply infrastructure, and continuing drought. However, the report notes that drought is not the chief cause of the region's water woes. It provides this stark assessment: "Today, in some areas of the West, existing water supplies are, or will be, inadequate to meet the water demands of people, cities, farms, and the environment even under normal water supply conditions."

The Water 2025 program proposes the following approaches to solving the West's looming water crises:

  • Modernizing the existing water supply infrastructure
  • Employing water conservation measures to more efficiently use existing water supplies
  • Establishing collaborative approaches and a market-based transfer system to minimize conflicts between water users
  • Conducting research in promising water technology treatment options, such as desalination

Irrigation withdrawals by state, 2000

The Bureau of Reclamation asked for $11 million in the fiscal year 2004 federal budget to fund the initiatives of the Water 2025 program.

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