Estimated Use of Water in the United States in 2000
This section has been revised since its initial release.
Trends in Water Use, 1950—2000
The USGS first conducted the water-use compilations for 1950 and has published them every 5 years since. Groupings of categories and data elements have changed through the years. Water-use categories were combined in some compilations and were published as separate categories in others. Summaries of withdrawal estimates from 1950 to 2000 are shown in table 14 and shown graphically in figures 13 and 14. Self-supplied domestic withdrawals are shown separately from livestock and aquaculture withdrawals in table 14, although these uses were combined in the rural domestic and livestock category in previous water-use Circulars and are shown together in figure 14.
The livestock category represents water use for farm animals (or stock) from 1950 through 1980. The livestock and aquaculture withdrawal estimates in table 14 include fish farms from 1985 through 2000. For 2000, this category includes water use for stock, fish farms and fish hatcheries in table 14.
The industrial category also has been treated differently in various compilation years. The industrial water-use data for 1960 through 1980 represented withdrawals for facilities traditionally considered industrial as well as water use by commercial and mining facilities, fish farms, and fish hatcheries. This combined category was called "other industrial use" to distinguish these uses from thermoelectric power generation water use. For the years 1985, 1990 and 1995, water-use data for industrial, commercial, and mining uses were published as separate categories. For 2000, industrial and mining withdrawals were compiled and published as separate categories, and commercial use was not compiled nationally. In table 14, commercial and mining withdrawals have been added to the industrial withdrawals for 1985 through 1995 so that the data are comparable to the "other industrial use" category in previous water-use Circulars. The "other industrial use" category cannot be calculated for 2000 because an estimate of commercial withdrawals was not compiled for 2000.
Estimates of withdrawals are summarized in table 14 at 5-year intervals from 1950 through 2000. The percentage change in withdrawals for each category (or category combination) is shown between 1995 and 2000. Estimates of total, ground-water, and surface-water withdrawals and total population are shown in figure 13. Figure 14 illustrates total freshwater and saline-water withdrawals by category.
Estimates in table 14 and figure 13 show total withdrawals increased steadily from 1950 to 1980, declined more than 9 percent from 1980 to 1985, and have varied less than 3 percent between the 5-year intervals since 1985. Total withdrawals peaked during 1980, although total U.S. population has increased steadily since 1950. Estimates of water use peaked during 1980 because of large industrial, irrigation, and thermoelectric-power withdrawals. Total withdrawals for 2000 were similar to the 1990 total withdrawals, although population had increased 13 percent since 1990.
Total withdrawals have remained about 80 percent surface water and 20 percent ground water during the 50-year period. The portion of surface-water withdrawals that was saline increased from 7 percent for 1950 to 20 percent for 1975 and has remained about 20 percent since. The percentage of ground water that was saline never exceeded about 2 percent. The percentage of total withdrawals that was saline water increased from a minor amount in 1950 to as much as 17 percent during 1975 and 1990.
Estimated withdrawals for public supply increased continually since 1950 (fig. 14) along with population served by public suppliers. Public-supply withdrawals more than tripled during this 50-year period and increased about 8 percent from 1995 to 2000. The percentage of population served by public suppliers increased from 62 percent for 1950 to 85 percent for 2000. Public-supply withdrawals represented about 8 percent of total withdrawals for 1950 and about 11 percent for 2000. The percentage of ground-water use for public supply increased from 26 percent for 1950 to 40 percent for 1985 and has remained at slightly less than 40 percent since.
Estimated withdrawals for self-supplied domestic use increased by 71 percent between 1950 and 2000. The self-supplied domestic population was 57.5 million people for 1950, or 38 percent of the total population. For 2000, 43.5 million people, or 15 percent of the total population, were self-supplied.
Withdrawals for livestock and aquaculture use increased from 1.5 Bgal/d during 1950 to 5.49 Bgal/d during 1995. The use for these categories during 2000 was 5.46 Bgal/d. The livestock and aquaculture estimate includes fish farms from 1985 through 2000. The water-use estimate for 2000 also includes fish hatcheries. Livestock water-use estimates for 2000 were not required from all States.
Since 1950, irrigation has represented about 65 percent of total withdrawals, excluding those for thermoelectric power. Withdrawals for irrigation increased by more than 68 percent from 1950 to 1980 (from 89 to 150 Bgal/d). Withdrawals have decreased since 1980 and have stabilized at between 134 and 137 Bgal/d between 1985 and 2000. Depending on the geographic area of the United States, this overall decrease can be attributed to climate, crop type, advances in irrigation efficiency, and higher energy costs.
Surface water historically has been the primary source for irrigation, although data show an increasing usage of ground water since 1950. During 1950, 77 percent of all irrigation withdrawals were surface water, most of which was used in the western States. By 2000, surface-water withdrawals comprised only 58 percent of the total. Ground-water withdrawals for irrigation during 2000 were more than three times larger than during 1950. Most of this increase occurred from 1965 through 1980.
The total number of acres irrigated in the United States steadily increased from 25,000 thousand acres for 1950 to 58,000 thousand acres for 1980. The estimated number of acres irrigated remained relatively constant from 1980 to 1995, and then increased to 61,900 thousand acres during 2000. The increase in irrigated acreage during the 1960s and 1970s was related to the expansion of irrigation in the western States. The number of acres irrigated in 2000 increased in some States in response to drought.
Since 1985, when USGS first collected data on irrigated acres by system type, more acres were irrigated using sprinkler and microirrigation systems than were irrigated with flood systems. The proportion of total acres irrigated using sprinkler and microirrigation systems increased from less than 40 percent in 1985 to 52 percent for 2000. The average irrigation application rate declined about 30 percent, from 3.55 acre-feet per acre during 1950 to 2.48 acre-feet per acre during 2000. The largest declines in application rates occurred after 1980.
Thermoelectric power has been the category with the largest water withdrawals since 1965, and for 2000 comprised 48 percent of total withdrawals. The largest total and fresh and saline surface-water withdrawals were during 1980. Withdrawals by thermoelectric-power plants increased from 40 Bgal/d during 1950 to 210 Bgal/d during 1980. Withdrawals for thermoelectric power declined and then stabilized since 1980; the total withdrawal of 195 Bgal/d for 2000 is the same as the total withdrawal for 1990.
Thermoelectric-power water withdrawals primarily were affected by the Federal legislation that required stricter water-quality standards for return flow and by limited water supplies in some areas of the United States (U.S. Congress, Amendments to the Federal Pollution Control Act of 1972 and 1977; Micheletti and Burns, 2002). Consequently, since the 1970s, power plants increasingly were built with or converted to closed-loop cooling systems or air-cooled systems instead of using once-through cooling systems. By 2000, an alternative to once-through cooling was used in about 60 percent of the installed steam-generation capacity in the power plants (Bozek, 2002).
Use of recirculated water for cooling in a closed-loop system reduces the water requirement at the power plant, resulting in reduced water withdrawals. The increasing influence over time of these technologies that require less water can be observed in the historical USGS water-use record. The trend showing the increase, decline, then stabilization of water withdrawals for thermoelectric power from 1950 to 2000 occurred as net electricity generated increased almost 15-fold to 3,450 billion kilowatt-hours (kWh) during this same period (U.S. Department of Energy, Energy Information Administration, 2003c). Overall, significantly less water was required to generate a kilowatt-hour of electricity for 2000. The average gallons of water used to produce one kilowatt-hour (gal/kWh) decreased from 63 gal/kWh during 1950 to 21 gal/kWh during 2000 (Solley and others, 1998).
The industrial category has been treated differently in various compilation years. The industrial water-use data for 1960 through 1980 represented use for facilities traditionally considered as industrial as well as water use for commercial and mining facilities, fish farms, and fish hatcheries. For the years 1985, 1990, and 1995, water-use data were published as the separate categories of industrial, commercial, and mining. For 2000, withdrawal data were compiled for industrial and mining uses but not commercial use. In table 14, commercial and mining withdrawals were added to the industrial withdrawals to correspond to the "other industrial use" category of previous water-use Circulars. Because commercial data were not available for 2000, a percentage change for 1995 to 2000 cannot be calculated for this combined category.
Withdrawals for "other industrial uses" were between 37 and 39 Bgal/d between 1950 and 1960, and then increased to the range of 45 and 47 Bgal/d for the years reported from 1965 to 1980. Withdrawals declined by about 32 percent to 30 Bgal/d between 1980 and 1985; the decline continued to about 29 Bgal/d in 1995. Because data were not classified separately from 1960 to 1980, it is not known how much of the "other industrial use" was attributable to commercial and mining withdrawals. However, it is evident that by 2000 the "other industrial use" category was at its lowest level since data were first reported for 1950. For the industrial withdrawals not to be at the lowest level since 1950, commercial water use, which was not reported for 2000, would have had to more than double between 1995 and 2000. That scenario for commercial water use is improbable.
Because withdrawal data were compiled independently for the industrial category for 1985 through 2000, the changes in the industrial category may be compared for those years. Total industrial withdrawals decreased by 24 percent from about 26 Bgal/d during 1985 to less than 20 Bgal/d during 2000. Ground water provided 15 percent of the total industrial withdrawals during 1985 and 18 percent of the total during 1990, 1995, and 2000. Almost all of the ground water withdrawn for industrial uses was freshwater. The percentage of surface water that is fresh has increased from about 84 percent during 1985 to about 92 percent during 2000.
Two factors have affected the industrial water-use withdrawals. Passage of the Amendments to the Federal Pollution Control Act of 1972 and 1977 required stricter water-quality standards for water discharges, which in turn, encouraged conservation, greater efficiency, and lower water- using technologies. Decline in the number of manufacturing facilities during more recent years also has reduced industrial withdrawals. Employment in two of the major water-using industries declined from 1985 to 2000. Employment in the petroleum and coal products industries declined by 26 percent, and employment in the primary metal industries declined by 13 percent (U.S. Department of Commerce, Bureau of Economic Analysis, 2003).
Water Use in the United States | USGS Water Resources of the United States
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