Water is an essential resource. It is also a nonrenewable or finite resource: While water supplies can be regenerated by creating new water molecules from their elemental beginnings (hydrogen and oxygen), the energy required to create large usable pools of water is currently too energy costly to be feasible. Threatening water resources are scarcity, overuse, and pollution. Variations in weather oscillations between wet and dry periods can result in periods of drought, increasing population demands can result in overuse, and continued multiple uses of water resources for industry, irrigation, drinking water, and wastewater can reduce the usability of the water resource for one or many of its needed uses. As we are inherently dependent upon our water resources, protecting and maintaining usable water supplies are critical to sustaining our ecological, cultural, social, and economic well-being.
The value of water as a resource is dependent upon the water’s intended use (function), supply, demand, and cost.
Water Resources Use
Off-stream use occurs when water is diverted away from its natural source (e.g., irrigation, thermoelectric power, industry, and public drinking water), while in-stream is the use of water in its place (e.g., boating and transportation, hydroelectric power, and recreation). In 2000, the generation of thermoelectric power accounted for 48 percent of off-stream water usage, followed by irrigation (34 percent); public water supply (11 percent); industry (5 percent); and domestic, livestock, aquaculture, and mining (3 percent). For most off-stream uses, water is consumed or not returned to the natural source. U.S. water consumption amounts to approximately 100 billion gallons daily.
Water Resources Supply
Water exists in two forms: seawater (97.5 percent) and freshwater (2.5 percent of the world’s water supply). Of the 2.5 percent of freshwater, 1.5 percent is in the polar ice sheets, 0.65 percent is in groundwater, and 0.35 percent is surface water (streams and lakes). U.S. water supplies include seawater, surface water (streams and lakes), and groundwater. Because seawater requires desalination before most of its off-stream uses, only Texas, Florida, and California consider seawater a viable water resource. The major sources of U.S. surface water are five major watersheds: the Columbia River Watershed (Northwest), the Mississippi River Watershed (Great Plains and Midwest), the Colorado River Watershed (Southwest), the Rio Grande Watershed (Southwest and Texas), and the St. Lawrence River Watershed (Great Lakes and Northeast). U.S. lakes and reservoirs hold approximately 26,550 cubic kilometers of water, with 22,573 cubic kilometers just in the Great Lakes. U.S. rivers hold approximately 250 cubic kilometers of water. U.S. groundwater comes from the many aquifers that underlie the landscape. The most heavily used aquifers are the High Plains or Ogallala Aquifer (Great Plains), the Central Valley aquifer system (California), the Mississippi River Valley alluvial aquifer (Mississippi River Valley), the Basin and Range basin-fill aquifers (West and Southwest), and the Floridan aquifer system (Florida).
Water Resources Demand
The demand for water continues to grow along with the population: In 1960 in the United States, total withdrawals were an estimated 175 billion gallons daily when the population was 179 million; in 2000, total withdrawals were an estimated 408 billion gallons daily for a population of 281 million. In the past 30 years, the U.S. population has grown 52 percent while total water usage has tripled. On average, Americans use 100 gallons per day for everything from drinking, bathing, laundry, and watering lawns. Water demand is greatest in the western United States where per capita use is roughly 50 percent greater than in eastern states. This disparity is due mostly to the large volume of water used for crop irrigation in California. Crop irrigation in California, Idaho, Colorado, and Nebraska accounted for more than half the total withdrawals for irrigation in 2000.
Water Resources Cost
With increasing demand, the cost of using and maintaining the nation’s water resources has increased. From the enactment of the Clean Water Act in 1972 to the year 1998, estimates from the U.S. Department of Commerce show that federal and local government expenditures for wastewater control increased from approximately $5 billion per year to $13 billion per year (in 1996 adjusted dollars). Overall, estimates place federal and private expenditures at over $540 billion on end-of-pipe water pollution control since 1972. The U.S. Environmental Protection Agency (EPA) also spent over $1 billion (1990-2000) to address nonpoint source pollution.
While these expenditures protect water resources, additional costs affect water usage. For instance, drinking water providers must constantly upgrade their plants with new technologies to remove a growing list of water contaminants regulated by the Safe Drinking Water Act. Advanced analytical methods make detection of other contaminants possible, such as pathogenic E. coli, human and veterinary medicines (e.g., antibiotics, steroids, and birth control hormones), personal care products, caffeine, pesticides, and herbicides—all found in both surface water and groundwater. Water treatment techniques such as ozonation, ultraviolet light treatment, activated carbon, or any combination of the three become exponentially costly as these systems also require upgrading to handle larger and larger demands. Plant upgrades can cost hundreds of millions of dollars. To assist with this need, EPA began the Drinking Water State Revolving Fund in 1997, which has since provided more than $9.5 billion worth of assistance to sustain the nation’s drinking water infrastructure. However, this is only a fraction of what is needed: EPA’s 1997 Drinking Water Infrastructure Needs Survey projected the necessity of a $138.4 billion investment over the next 20 years to ensure the continued source development, storage, treatment, and distribution of safe drinking water. Additionally, not only are our source waters threatened by scarcity and pollution, but distribution systems for clean and safe water are under growing security threats (e.g., terrorism). In 2006, EPA had a budget of $33 million to protect drinking water from terrorist attacks. The cumulative effect of these costs is reflected in the national per gallon cost of water. On average, U.S. consumers pay $2.00 for every 1,000 gallons of water. On the whole, 4 percent of the nation’s energy goes to treating and moving drinking water and wastewater.
- Hutson, Susan S., Nancy L. Barber, Joan F. Kenny, Kristin S. Linsey, Deborah S. Lumia, and Molly A. Maupin. 2004. Estimated Use of Water in the United States in 2000. Circular 1268. Reston, VA: U.S. Geological Survey.
- Maupin, Molly A. and Nancy L. Barber. 2005. Estimated Withdrawals from Principal Aquifers in the United States, 2000. Circular 1279. Reston, VA: U.S. Geological Survey.
- Miller, James A. 2000. Ground Water Atlas of the United States. Reston, VA: U.S. Geological Survey. Retrieved March 27, 2017 (https://water.usgs.gov/ogw/aquifer/atlas.html).
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