Ground water constitutes most of the earth's usable water resources. The total amount of water on the earth is estimated at 326 million cubic miles. Of this total, more than 97% is sea water. An appreciable part of the world's total water, 2%, is frozen in ice caps and glaciers. Virtually all of the remaining water is ground water. The water in rivers and lakes (which scientists call surface water), in the atmosphere, and in unsaturated soils and rocks amounts to only about one-fiftieth of 1% of the total world water supply at any given moment. Ground water accounts for about 2 million cubic miles, or about 0.6% of the earth's total water. If we exclude ice, ground water represents about 97% of the non-ocean water. About half of the ground water occurs within the upper half mile of the earth's crust, and the remainder below this depth. Not all of it is usable; some is saline, and some can be regarded as inaccessible because of the great depths at which it occurs. Nor is it uniformly distributed over the land areas of the world. In many places, ground water cannot be obtained in sufficient quantities to justify the expense of installing wells.
In some areas, including parts of Kansas, ground water is the only reliable source of large volumes of water. Kansans rely on ground water for 85% of their water needs, including municipal, industrial, agricultural, and rural domestic water supplies. In fact, Kansas relies on ground water to supply a higher percentage of its water needs than almost any other state in the U.S. Eastern and western Kansas differ dramatically in their reliance on ground water. In the western two-thirds of the state, where precipitation amounts are usually small, relatively abundant ground-water resources provide most of the water. Ground-water resources are limited in the eastern third of the state, but precipitation is more abundant and surface water provides most of the water supplies. Ground water supplies approximately 4.8 billion gallons per day. Municipal and rural-water supply systems provide ground water to approximately 51% of the state's population (1.2 million people). Approximately 94% of the ground water withdrawn (4.5 billion gallons per day) is used for irrigation, 2% for industry, 3% for public municipal supplies, 0.5% for livestock use, and 0.4% for rural domestic use. Water-use figures in this paragraph are from C. H. Baker, Jr., and J. F. Kenny, "Kansas: Water Supply and Use;" in, U.S. Geological Survey, National Water Summary 1987, Water-Supply Paper 2350, 1990.
These numbers provide perspective on water use. Domestic use (municipal plus rural) amounts to about 160 gallons per day (or gpd) per person, fairly typical for the U.S. We know that adequate life support requires less than a tenth of that amount; experience in areas of water shortage has shown that conservation measures can reduce that 160 gpd by about half without health or serious economic consequences. On the other hand, if we divide total water use (including agricultural and industrial as well as domestic) by total population, the state's total use rate is about 2,800 gpd per person. This very large difference between individual use and collective use represents water used in economic activities, of which irrigated agriculture is by far the largest consumer. Figure 1 shows a breakdown of water use by source and type of use.
Figure 1--Percent of total ground-water use in Kansas going to various applications in 1987 (USGS, Water-Supply Paper 2350, 1990).
Definitions of italicized words are linked to the glossary in appendix A.
Kansas Geological Survey, Kansas Ground Water
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Web version Jan. 2005. Original publication date August 1993.