Q: How do the three primary global human water-use sectors (agriculture, industry and municipal supply) compare in terms of withdrawal and actual water consumption?
A: These values vary somewhat from country to country and from the less developed to more developed countries. In general, about 70% of the water withdrawn from freshwater sources globally supports agriculture, while about 20% supports industrial activities and 10% is used for municipal supplies. Water withdrawal and consumption are not the same metric and a much greater percentage of the water withdrawn for agriculture is actually consumed as irrigation water while a much smaller percentage of water withdrawn to support industrial and municipal supply is actually consumed and rendered unavailable for other uses. Worldwide, about 93% of the water consumed by humans goes to irrigated agriculture, while about 4% and 3%, respectively, are consumed by industry and municipal uses.
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Q: How much water is used for irrigation per year in the United States?
A: According to USGS data from their 2000 survey, water withdrawal for irrigation uses was estimated at 137,000 million gallons per day. This is equivalent to almost 2.5 acre-feet of water per acre irrigated. Irrigation use in 2000 accounted for about 40% of total freshwater withdrawals or 65% of all withdrawals with exclusion of thermoelectric power generation. See Estimated Use of Water in the United States in 2000 for more information about irrigation and other water uses.
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Q: How much freshwater withdrawal goes to agricultural uses in the U.S., and what does this include?
A: Agricultural water use can be divided between irrigation and livestock. Irrigation includes all water applied to farm or horticultural crops; livestock incorporates water used for livestock, dairies, feedlots, fish farms, and other farm needs. Estimated annual water use for irrigation has remained at about the same level since 1985, with approximately 63% of the water used for irrigation coming from surface water. Approximately 60% of the water used for livestock comes from ground water sources and the remaining 40% from surface water sources. Combined water use for irrigation and livestock represents about 41% of total offstream freshwater use, with 40% going to irrigation and the lone 1% to livestock uses. Not only can the loss of water from irrigation conveyance systems be significant, but the percentage of consumptive water use for agriculture is high. Consumptive use is estimated at 56% for irrigation and 67% for livestock uses.
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Q: How much water is used in the United States each day for irrigation of crops?
A: Daily irrigation use is much larger than drinking water use (about four times), but the volume depends on the location and the time of year. It takes about 50 glasses of water just to grow enough oranges to produce one glass of orange juice, for example. One estimate puts the total amount used for irrigation at 141 billion gallons a day, 66% from surface water and 34% from groundwater. Of course, most irrigation water is not treated as tap water is. Total industrial use, by comparison, is about 160 billion gallons per day.
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Q: Which states have the most irrigated acres in the United States?
A: As of 2007, Nebraska had the most irrigated land at 8.5 million acres. California was second at just over 8 million acres. Texas was 3rd at 5 million acres, followed by Arkansas at 4.4 million. Idaho and Colorado have approximately 3 million each. The only states within the southeast with over a million acres in irrigation are Florida with about 2.2 million and Georgia with about 1.2 million acres. Utah has over 1.3 million acres in irrigation and the states of South Dakota, Michigan, North Carolina and Hawaii have over 100 thousand acres in irrigation but less than half a million.
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Q: How much water is there in an acre-foot and why is this term often used to measure large volumes of water?
A: The official standard quantity of water in an acre-foot is 325,851 gallons. However, for most purposes this value is generally rounded off to 326,000 gallons. An acre-foot is the quantity of water that will cover an acre of land surface, our official land area measurement in the United States, to a depth of one foot. This term is commonly used in the U.S. because it is convenient for estimating water storage volume in lakes and reservoirs based on surface area of the particular water body and its average depth in feet. It is also a convenient term for agricultural irrigation, which is usually measured and applied as inches per acre. Of course, an acre-foot will contain 12 acre-inches of water. An acre-inch of water is equivalent to 27,154 gallons, but this value is often rounded off to 27,000. Many other water users, including municipal authorities, have adopted the acre-foot as a unit for measuring large volumes of water. City water meters are often designed to measure units of cubic feet. In looking at your water bill, you may find that your cost is based on how many units of 1000 cubic feet you used during any given month. Water use, storage and system distribution needs in cubic feet can be readily related to water supply needs in acre-feet of storage in a source reservoir. One acre-foot contains 43,560 cubic feet of water and one cubic foot contains 7.48 gallons, which is often rounded off to 7.5.
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Q: What is a drought?
A: A drought is a sustained and regionally extensive occurrence of appreciably below-average natural water availability in the form of precipitation, streamflow, or groundwater. Droughts are natural events of varying duration that have occurred throughout history and they are part of the cyclical fluctuations of our planet’s climate system.
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Q: I have a senior water right and always have enough water. Why should I worry about improved irrigation efficiency?
A: Improved efficiency can benefit senior users by reducing pumping costs, prolonging the life of aquifers, reducing waterlogging, maintaining nutrients and pesticides in the rootzone.
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