Where does irrigation water come from and how is it applied to the land?
Both ground water and surface water are used for irrigation. In 1990, about 51,000 million gallons per day were withdrawn from the ground for irrigation, whereas about 85,500 million gallons per day was taken from surface-water sources. A small amount of reclaimed wastewater coming from sewage-treatment plants, about 660 million gallons per day was used for irrigation. The USGS keeps records on the types of irrigation systems used in the United States. One method is called flood irrigation, where water flows onto the land. Another method is called spray irrigation where water is sprayed or dripped on the crops. In 1990, about 34,500,000 acres out of the 57,400,000 total irrigated acres (about 60 %), were irrigated by the flood process. The other 40 % of land was spray irrigated.
