Irrigation water use

Think of what your supper table might be like if water was not used to irrigate crops. Do you think you could survive very long without heaping servings of eggplant, beets, brussels sprouts, and rutabagas? Irrigation water is essential for keeping fruits, vegetables, and grains growing to feed the world's population, and this has been a constant for thousands of years.

Throughout the world, irrigation (water for agriculture, or growing crops) is probably the most important use of water (except for drinking and washing a smelly dog, perhaps). Estimates vary, but about 70 percent of all the world's freshwater withdrawals go towards irrigation uses (http://www.globalagriculture.org/report-topics/water.html). Large-scale farming could not provide food for the world's large populations without the irrigation of crop fields by water gotten from rivers, lakes, reservoirs, and wells. Without irrigation, crops could never be grown in the deserts of California, Israel, or my tomato patch.

Irrigation has been around for as long as humans have been cultivating plants. Man's first invention after he learned how to grow plants from seeds was probably a bucket. Ancient people must have had strong backs from having to haul buckets full of water to pour on their first plants. Pouring water on fields is still a common irrigation method today—but other, more efficient and mechanized methods are also used. One of the more popular mechanized methods is the center-pivot irrigation system, which uses moving spray guns or dripping faucet heads on wheeled tubes that pivot around a central source of water. The fields irrigated by these systems are easily seen from the air as green circles. There are many more irrigation techniques farmers use today, since there is always a need to find more efficient ways to use water for irrigation

When we use water in our home, or when an industry uses water, about 90 percent of the water used is eventually returned to the environment where it replenishes water sources (water goes back into a stream or down into the ground) and can be used for other purposes. But of the water used for irrigation, only about one-half is reusable. The rest is lost by evaporation into the air, evapotranspiration from plants, or is lost in transit, by a leaking pipe, for example.

Irrigation water withdrawals for the Nation, 2005

For 2005, total irrigation withdrawals were about 128,000 million gallons per day (Mgal/d), or 144,000 thousand acre-feet per year. (All 2010 water use information is from the report Estimated use of water in the United States in 2010.) Irrigation withdrawals were 37 percent of total freshwater withdrawals and 62 percent of total freshwater withdrawals for all categories, when excluding thermoelectric power. Surface water accounted for 58 percent of the total irrigation withdrawals. About 61.1 million acres were irrigated in 2005.

About 26.6 million acres were irrigated with surface (flood) systems, 4.05 million acres with microirrigation systems, and 30.5 million acres with sprinkler systems. The national average application rate was 2.35 acre-feet per acre.

Irrigation water withdrawals, by State, 2005

The majority of withdrawals (85 percent) and irrigated acres (74 percent) were in the 17 conterminous Western States. The 17 Western States are located in areas where average annual precipitation typically is less than 20 inches and is insufficient to support crops without supplemental water. Surface water was the primary source of water in the arid West and the Mountain States. California, Idaho, Colorado, and Montana combined accounted for 49 percent of the total irrigation withdrawals and 64 percent of surface-water irrigation withdrawals. Nearly 90 percent of the groundwater used for irrigation was withdrawn in 13 States, and each of these States withdrew more than 1,000 Mgal/d (1,120 thousand acre-feet per year) of groundwater for irrigation in 2005. Among these 13 States, groundwater was the primary source for irrigation in Nebraska, Arkansas, Texas, Kansas, Mississippi, and Missouri.

Total irrigation withdrawals in both Eastern and Western States were smaller in 2005 than in 2000, but because the West accounts for such a large majority of the total, changes in those States have a greater effect on the total. Groundwater withdrawals increased slightly in the East, and surface-water withdrawals declined in both the East and West. Total irrigated acres decreased in the West by 4 percent and increased in the East by 5 percent. In the West, acres irrigated by surface irrigation methods declined by 16 percent, and acres irrigated by sprinkler methods increased by 9 percent. Irrigated acres in the East increased for all type of systems; the largest percentage increase was in microirrigation systems.

Five States—California, Nebraska, Texas, Arkansas, and Idaho—accounted for 52 percent of total irrigated acreage. Nebraska, Texas, and California accounted for 41 percent of the irrigated acreage using sprinkler and microirrigation systems. California alone accounted for 65 percent of the irrigated acreage with microirrigation systems. Sprinkler and microirrigation systems combined were associated with more than 56 percent of total irrigated acreage.

Trends in irrigation water withdrawals, 1950-2005

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 89,000 to 150,000 Mgal/d). Withdrawals have decreased since 1980 and have stabilized at between 134,000 and 137,000 Mgal/d between 1985 and 2000, and 128.000 in 2005 . 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 groundwater since 1950. During 1950, 77 percent of all irrigation withdrawals were surface water, most of which was used in the western States. By 2005, surface-water withdrawals comprised only 59 percent of the total. Groundwater withdrawals for irrigation during 2005 were more than three times larger than during 1950. Most of this increase occurred from 1965 through 1980.

Irrigation water use, 2000

• Estimated Use of Water in the United States in 2000, USGS Circular 1268:
• Irrigation water use, 2000: Summary | Data table, by State | National map