Agricultural Water Supply

Irrigation and livestock are the two main water uses in agriculture. Irrigation includes all water applied to the farm or to horticultural crops. Livestock water uses include water for livestock, dairies, feedlots, fish farms, and other farm needs.

Approximately 63% of the water used for irrigation in the U.S. in 1990 came from surface water, while about 60% of the water used for livestock came from groundwater sources. Combined water use for irrigation and livestock accounted for approximately 41% of total offstream freshwater use for 1990, of which 40% was used for irrigation and only 1% for livestock uses.

Agriculture is the largest consumer of water nationally. In 1980, irrigation accounted for 97% of this use, with the remainder going to rural domestic use and livestock production. There have been serious depletions of some regional aquifers, due to groundwater withdrawals for irrigation, particularly in western areas. The Ogallala aquifer, for example, has dropped from an average saturated water thickness of 58 feet in 1930 to a thickness of approximately 8 feet in the late 1980s. Surface water depletion from irrigation is also a major concern in the western states. In Michigan, groundwater is found in both bedrock and glacial aquifers. Approximately 70% of the water withdrawn from both groundwater and inland lakes and streams in Michigan is used for irrigation.

Nationwide consumptive water use for irrigation is projected to increase from 83 bgd to 93 bgd in the year 2000. Supply augmentation is not feasible in many places because of economic and environmental constraints. Various methods for conserving and reusing irrigation waters include development of more productive and/or salt-tolerant crop species; increased use of chemical fertilizers, pesticides, and herbicides; lining of irrigation canals or the use pipelines to prevent seepage loss; "trickle" or "drip" irrigation practices to reduce the quantity of water necessary for continued crop yield; and the reuse of municipal and/or agricultural wastewater for direct irrigation. (Dzurik 1990)