Considering the entire hydrosphere, or all of Earth's water, only as be about six tenths of 1 percent occurs underground. Nevertheless, this small percentage, stored in the rocks and sediments beneath Earth's surface, is a vast quantity, When the oceans are excluded and only sources of freshwater are considered, the significance of groundwater becomes more apparent.
Table 5.2 contains estimates of the distribution of freshwater in the hydrosphere. Clearly, the largest volume occurs as glacial ice. Second in rank is groundwater, with slightly more than l4 percent of the total. However, when ice is excluded and just liquid water is considered, more than 94 percent is groundwater. Without question groundwater represents the largest reservoir of freshwater that is readily available to humans. Its value in terms of economics and human well-being is incalculable.
Worldwide, wells and springs provide water for cities, crops, livestock, and industry. In the United States, ground water supplies nearly one-quarter of our freshwater needs- about 80 billion gallons per day. In some areas, however, overuse of this basic resource has caused serious problems, including streamflow depletion, land subsidence, and in creased pumping costs. In addition, groundwater contamination due to human activities is a real and growing threat in many places.
Considering the entire hydrosphere, or all of Earth's water, only as be about six tenths of 1 percent occurs underground. Nevertheless, this small percentage, stored in the rocks and sediments beneath Earth's surface, is a vast quantity, When the oceans are excluded and only sources of freshwater are considered, the significance of groundwater becomes more apparent. Table 5.2 contains estimates of the distribution of freshwater in the hydrosphere. Clearly, the largest volume occurs as glacial ice. Second in rank is groundwater, with slightly more than l4 percent of the total. However, when ice is excluded and just liquid water is considered, more than 94 percent is groundwater. Without question groundwater represents the largest reservoir of freshwater that is readily available to humans. Its value in terms of economics and human well-being is incalculable. Worldwide, wells and springs provide water for cities, crops, livestock, and industry. In the United States, ground water supplies nearly one-quarter of our freshwater needs- about 80 billion gallons per day. In some areas, however, overuse of this basic resource has caused serious problems, including streamflow depletion, land subsidence, and in creased pumping costs. In addition, groundwater contamination due to human activities is a real and growing threat in many places.
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