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Estimated use of water in the United States in 1990
Trends in Water Use

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Trends in water use, 1950-1990

To facilitate the following discussion of trends in water use, the estimates for some categories used in this report have been combined to correspond to the categories used in previous water-use circulars in this series (public supply, rural use, irrigation, industrial, thermoelectric power, hydroelectric power). Self-supplied domestic withdrawals were combined with livestock withdrawals in this section of the report to compare to the rural use category listed in previous water-use circulars; and self-supplied industrial withdrawals were combined with commercial and mining withdrawals to compare to " other" industries, which were listed with thermoelectric power generation under self-supplied industrial in previous water-use circulars.

Data in table 31 summarize the estimated water use---withdrawals, source of water, reclaimed wastewater, consumptive use, and instream use (hydroelectric power)---at 5-year intervals from 1950 to 1990. Table 31 below also shows the percentage increase or decrease in the summarized estimates between 1985 and 1990.

After continual increases in estimates of the Nation's water use from 1950 to 1980, offstream and instream uses were less during 1985 than during 1980. Total offstream use during 1990 was 2 percent more than the 1985 estimate, but still 8 percent less than the 1980 estimate. Instream use during 1990 was 8 percent more than the 1985 estimate, or about the same as the 1975 and 1980 estimates, as shown graphically in figure 33 (GIF file), or as a PostScript file (72K). For most water-use categories, the general slackening in the rate of increase that had been indicated by the estimates compiled for 1975 and 1980 changed to a decrease in water use between 1980 and 1985 (figure 34 (GIF file), or as a PostScript file (70 Kb)). Total withdrawals were about 10 percent less during 1985 than during 1980, and the 2 percent increase from 1985 to 1990 is the result of increases in surface- and ground-water withdrawals of 1 and 9 percent, respectively. The fact that the 1990 withdrawal estimates are only slightly higher than the 1985 estimates tends to confirm the overall decline in water use from the peak of 1980.

Two exceptions to this decreasing trend are the "Public supply" and "Thermoelectric power" categories. Withdrawals for both of these categories were about 5 percent more during 1990 than during 1985. The 5-percent increase in public-supply withdrawals corresponds to a 4-percent increase in population served, and the increase in thermoelectric power water use reflects increases in power production.

Total irrigation withdrawals were about the same during 1960 as during 1955, then increased progressively for the years reported from 1965 to 1980. Estimated irrigation withdrawals during 1985 reversed that trend, however, and were 9 percent less than during 1980 and were about the same during 1990 as 1985. The increase in estimated ground-water withdrawals from 1985 to 1990 was partly the result of decreased availability of surface water. Surface-water withdrawals for irrigation increased progressively for the years reported from 1960 to 1985 and decreased 6 percent from 1985 to 1990. The average amount of water applied per acre for irrigation in the United States during 1985 and 1990 was about 2.7 acre-ft and less than the 2.9 acre-ft applied during 1975 and 1980. The rate of increase in the number of acres irrigated has been decreasing. The acreage reported for 1970 was about 14 percent more than in 1965; for 1975, 8 percent more than for 1970; for 1980, 7 percent more than for 1975; for 1985, about 1 percent less than for 1980; and for 1990, about the same as for 1985.

Table 31.   Trends of estimated water use in the United States,  1950-90.

[Data for 1950-80 adapted from MacKichan (1951, 1957), MacKichan and Kammerer (1961), Murray (1968), Murray and Reeves (1972, 1977), and Solley and others (1983, 1988). The water-use data are in thousands of million gallons per day and are rounded to two significant figures for 1950-80, and to three significant figures for 1985-90; percentage change is calculated from unrounded numbers. Numbers in parentheses indicate footnotes.]

Year Percentage change --------------------------------------------------------------------------------------- (1) (1) (2) (2) (3) (4) (4) (4) (4) 1950 1955 1960 1965 1970 1975 1980 1985 1990 1985-90 --------------------------------------------------------------------------------------- Population, in millions ........ 150.7 164.0 179.3 193.8 205.9 216.4 229.6 242.4 252.3 +4 Offstream use: Total withdrawals ........... 180 240 270 310 370 420 (5)440 399 408 +2 Public supply ............ 14 17 21 24 27 29 34 36.5 38.5 +5 Rural domestic, livestock. 3.6 3.6 3.6 4.0 4.5 4.9 5.6 7.79 7.89 +1 Irrigation ............... 89 110 110 120 130 140 150 137 137 -.3 Industrial: Thermoelectric power use 40 72 100 130 170 200 210 187 195 +4 Other industrial use ... 37 39 38 46 47 45 45 30.5 29.9 -2 Source of water: Ground: Fresh .................. 34 47 50 60 68 82 (5)83 73.2 79.4 +8 Saline ................. (*6) .6 .4 .5 1 1 .9 .652 1.22 +87 Surface: Fresh .................. 140 180 190 210 250 260 290 265 259 -2 Saline ................. 10 18 31 43 53 69 71 59.6 68.2 +14 Reclaimed wastewater ......... (6) .2 .6 .7 .5 .5 .5 .579 .750 +30 Consumptive use .............. (6) (6) 61 77 (7)87 (7)96 (7)100 (7)92.3 (7)94.0 +2 Instream use: Hydroelectric power ........ 1,100 1,500 2,000 2,300 2,800 3,300 3,300 3,050 3,290 +8 --------------------------------------------------------------------------------------------------------------- Footnotes: (1) 48 States and District of Columbia. (5) Revised (2) 50 States and District of Columbia. (6) Data not available. (3) 50 States and District of Columbia, and Puerto Rico. (7) Freshwater only. (4) 50 States and District of Columbia, Puerto Rico, and Virgin Islands.

To compare self-supplied industrial withdrawals during 1990 with comparable withdrawals for "other" industrial uses during earlier years, the 1990 estimates for industrial withdrawals need to be combined with those for commercial and mining withdrawals. Estimates of total self-supplied withdrawals (fresh, saline) for "other" industrial uses during 1990 were 29,900 Mgal/d, or about 2 percent less than during 1985, which was 34 percent less than during 1980, after remaining about the same during 1970, 1975, and 1980. In fact, self-supplied withdrawals for "other" industrial use during 1990 were the lowest reported in this series since records began in 1950. Surface-water withdrawals for industrial uses during 1990 totaled 21,800 Mgal/d, an 8-percent decrease from 1985; ground-water withdrawals totaled about 8,000 Mgal/d, a 20-percent increase from 1985.

More water continues to be withdrawn for thermoelectric power generation than for any other category, even though about the same quantity of freshwater was withdrawn for this use during 1990 as during 1985 ( figure 34 (GIF file), or as a PostScript file (70 Kb)). The 4-percent increase in total withdrawals for thermoelectric power from 1985 to 1990 is the result of a 15-percent increase in saline-water withdrawals.

Water used for hydroelectric power generation had been increasing steadily from 1950 to 1975, but, during 1980, it was about the same as during 1975. Water use for hydroelectric power generation during 1985 was 7 percent less than during 1980, and then was 8 percent more during 1990 than during 1985. Changes in hydroelectric power water use are closely related to the availability of surface water.

Even though population increased 4 percent between 1985 and 1990, withdrawal and consumptive-use estimates increased only 2 percent between 1985 and 1990. This is in contrast to 1970 and 1975, when the rate of increase in withdrawals was more than double the rate of population growth.

The trends in water use from 1950 to 1990 can be attributed in part to the following factors:

Several agencies and commissions have made projections of national water use to the year 2000 and beyond. The most recent study by the United States Department of Agriculture Forest Service (1989) projects water withdrawals and consumptive use to the year 2040. The projections by these agencies and commissions vary greatly reflecting the availability of reliable data and reflecting different assumptions for future population growth, economic conditions, energy-resources development, and environmental regulations.

Projections of future water use are beyond the scope of this report, although the trends established over the past 40 years provide some basis for estimating future water demands. It seems likely that water withdrawals for public supply and domestic uses will continue to increase as population increases. However, higher water prices and active water conservation programs may reduce the per-capita use rate. With increased competition for water for instream uses, such as river-based recreation, esthetic enjoyment, fish and wildlife habitat, and hydroelectric power, along with higher municipal uses, irrigators will have increasing difficulty competing economically for available water supplies. Municipal and industrial users can afford to pay much more for water than the farmers. Thus, a leveling in the rate of agricultural water use combined with growing population and urbanization suggests that, for the foreseeable future, new balances will have to be struck in water use between the rural and urban areas, especially in the western United States (Moore and others, 1990, p. 97). It seems likely that, for the foreseeable future, industrial water use and use per unit of production will continue to decline in most sectors, although probably not as sharply as in the recent past (David and others, 1990, p. 85).

Water management in the United States has traditionally focused on manipulating the country's vast supplies of freshwater to meet the needs of users. The effects of this "supply management" approach have been felt in every sector of the economy, from municipal water supply to irrigation. Increasing development costs, capital shortages, government fiscal restraint, less favorable storage reservoir sites, and increasing concern for the environ- ment have forced water managers to begin to rethink traditional approaches to water management and to experiment with new ones. Experts on the subject of western water agree that the West is in transition from the era of water development to an era of water management and conservation (Wilkinson, 1985). Attention now and in the future will be centered on optimizing the use of existing surface-water projects rather than on the further development of large storage reservoirs and major aqueducts, on developing more efficient water application techniques, and on developing other water conservation measures such as lining irrigation canals and installing more efficient plumbing fixtures in homes and office buildings.

Regardless of which projection proves correct, major attention needs to be given to water-management problems to ensure that maximum benefits will be obtained from use of the Nation's water resources. This has become more evident, because, in addition to the need for an adequate water supply, water-quality conditions need to be suitable if supply and demand are to be kept in balance.

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