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The Ground Water Supply and Its Use/
Ground water is a significant water supply source. The amount of ground water storage dwarfs our present surface water supply. At any given moment it is 20 to 30 times greater than the amount in all the lakes, streams, and rivers of the United States. Ground water is also an important source of surface water. It also adds about 492 billion gallons per day to U.S. surface water bodies. Its contribution to the overall flow of rivers and streams in the U.S. may be as large as 50 percent, and it is a major source of water for lakes and wetlands.
Ground water is tapped through wells placed in water-bearing
soils and rocks beneath the surface of the earth. Of the total 341
billion gallons of fresh water the United States withdraws each
day, ground water is estimated to be 83.213 billion gallons, or
24 percent. There are nearly 16 million water wells in the U.S.,
supplying ground water for public supply, private supply, irrigation,
livestock, manufacturing, mining, thermoelectric power, and other
purposes.
The National Ground Water Association has determined that 47 percent of the U.S. population depends on ground water for its drinking water supply from either a public source or private well. In the Asia-Pacific region, 32 percent of the population is ground water dependent; in Europe, 75 percent; in Latin America, 29 percent; and in Australia, 15 percent.
There are 107,846 community supply wells in the United
States. These are wells for 41,264 community distribution systems.
In comparison, there are 15.4 million individual households served
by private wells. Approximately 800,000 boreholes are drilled in
the U.S. annually. The construction of these vitally needed water
supply systems involves the use of more than 19,000 drilling rigs
by an estimated 8,000 ground water contracting firms.
The U.S. is one of the largest water well markets
in the world:
- India—21 to 25 million wells
- United States—15.9 million
- China—3.4 million
- Bangladesh—800,000
- Pakistan—700,000
- Germany—500,000
- South Africa—500,000
- Nepal—60,000
- Taiwan—37,100
- Mongolia—27,000
- Botswana—7,500
- Costa Rica—5,000
Private household wells constitute the largest share of all water wells in the U.S. Other kinds of wells are used for municipal systems, industry, agriculture, and water quality monitoring. Michigan, with 1,121,075 households served by private water wells, is the largest state market, followed by:
- Pennsylvania—978,202 households
- North Carolina—912,113
- New York—824,342
- Florida—794,557
Irrigation accounts for the largest use of ground water in the U.S.—49 billion gallons. Nebraska leads the nation in the number of irrigation wells in use with 69,583. Other leading irrigation well states are:
- California—64,423 irrigation wells
- Texas—59,955
- Arkansas—35,574
- Missouri—10,913
- Kansas—19,124
- Florida—16,376
Ground water is a renewable resource. In most parts of the United States, water removed from the ground is constantly replaced, although in some parts of the country such as arid and semiarid regions, a low rate of replenishment is far exceeded by the rate of ground water pumping, resulting in serious problems of ground water mining. Adequate time is needed to allow replenishment of underlying ground water reservoirs (aquifers); also such areas must be properly managed in order to prevent water-soluble waste products stored in these areas from infiltrating and polluting the underground supply.
Figures are current as of August 9, 2005.
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