Article

Background
Thermoelectric
Irrigation
Public Supply

Industrial
Other
Trends in Water Use

We use water every day—for drinking, for watering our lawns and gardens, for recreation, and for many uses that we don't necessarily see but which are critical to our lives. Large quantities of water are used to generate power and to cool electricity-generating equipment. Water is used for irrigation, aquaculture, and for many industrial processes and commercial uses. Our nation's underground and surface waters are vitally important to our everyday life.

Since 1950, the U.S. Geological Survey (USGS) has compiled data on amounts of water used in homes, businesses, industries, and on farms throughout the United States, and has described how that use has changed with time. Water-use data are collected at five-year intervals. These data, combined with other USGS information, have facilitated a unique understanding of the effects of human activity on the Nation's water resources. Water availability has emerged as an important issue for the 21st century and, as a result, the need is increasing for consistent, long-term water-use data to support wise use of this essential natural resource.

Between 1950 and 1980 there was a steady increase in water use in the United States. During this time, the expectation was that as population increased, so would water use. Contrary to expectation, reported water withdrawals declined in 1985 and have remained relatively stable since then in spite of a steady increase in United States population. Changes in technology, in State and Federal laws, and in economic factors, along with increased awareness of the need for water conservation, have resulted in more efficient use of the water from the Nation's rivers, lakes, reservoirs, and aquifers.

Estimates of water use for 2000 indicate that about 408 billion gallons per day (abbreviated Bgal/d) were withdrawn for all uses during the year. This total has varied less than 3 percent since 1985 as withdrawals have stabilized for the two largest uses—thermoelectric power and irrigation. Freshwater withdrawals were about 80 percent of the total, and the remaining 20 percent was saline water. Saline water is defined as water with 1000 mg/L or more of dissolved solids; it is usually undesirable for drinking and for many industrial uses.

Cooling towers, Burke County, Georgia.
Credit: U.S. Geological Survey Thermoelectric power accounts for about half of total water withdrawals. Most of the water is derived from surface water and used for once-through cooling at power plants. About 52 percent of fresh surface-water withdrawals and about 96 percent of saline-water withdrawals are for thermoelectric-power use.

Grated-pipe flood irrigation, Fremont County, Wyoming.
Credit: USDA, Natural Resources Conservation Service Irrigation accounts for about a third of water use and is currently the largest use of fresh water in the United States. Irrigation water use includes water used for growing crops, frost protection, chemical applications, weed control, and other agricultural purposes, as well as water used to maintain areas such as parks and golf courses. Historically, more surface water than ground water has been used for irrigation. However, the percentage of total irrigation withdrawals from ground water has continued to increase, from 23 percent in 1950 to 42 percent in 2000. Irrigated acreage more than doubled between 1950 and 1980, then remained constant before increasing nearly 7 percent between 1995 and 2000. The number of acres irrigated with sprinkler and microirrigation systems has continued to increase and now comprises more than one-half the total irrigated acreage.

Combined withdrawals for self-supplied domestic, livestock, aquaculture, and mining activities represented about 3 percent of total water withdrawals for 2000. Self-supplied domestic withdrawals include water used for household purposes which is not obtained from public supply. About 43 million people in the United States self-supply their domestic water needs, usually from wells. Livestock water use includes watering, feedlots, and other on-farm needs for animals such as cattle, sheep, pigs, horses, and poultry. Aquaculture use is water used for fish hatcheries, fish farms, and shellfish farms. Mining water use encompasses water used for the extraction of minerals, including solids such as coal and ores, liquids such as crude petroleum, and gases such as natural gas. Also included is water used for processes done as part of the mining activity. Nearly all of saline ground-water withdrawals in 2000 were for mining.

Total withdrawals have remained about 80 percent surface water and 20 percent ground water since 1950. The portion of surface-water withdrawals that was saline increased from 7 percent for 1950 to 20 percent for 1975 and has remained about 20 percent since. The percentage of ground water that was saline never exceeded about 2 percent. The percentage of total withdrawals that was saline water increased from a minor amount in 1950 to as much as 17 percent during 1975 and 1990.

More detailed information on water-use and water-use trends is available in the U.S. Geological Survey publication Estimated Use of Water in the United States in 2000 . Water basics and additional water-use information can be found in USGS: Water Science for Schools , especially the Water Questions & Answers.