Worldwide,
agriculture is the single biggest drain on water supplies, accounting for about
69 percent of all use. About 23 percent of water withdrawals go to meet the
demands of industry and energy, and just 8 percent to domestic or household use.
3 Patterns of use vary greatly from country to country, depending on
levels of economic development, climate and population size. Africans, for
instance, devote 88 percent of the water they use to agriculture, mostly
irrigation, while highly-industrialized Europeans allot more than half their
water to industry and hydroelectric energy production.
Although
much of the world's farming still relies on the renewable water that falls on
crops from the sky, irrigation largely explains agriculture's thirst. And the
watering of crops has grown in tandem with rising world population. (Livestock
production is an agricultural activity, but its use of water is minor compared
to irrigation.) In 1990, 250 million hectares (620 million acres) of land were
under irrigation worldwide, supplying a third of the world's harvested crops, 8
and agriculture was the primary use for water in two out of three countries.
3
Agricultural
water use is particularly high in arid areas such as the Middle East, North
Africa and the southwestern United States, where rainfall is minimal and
evaporation so high that crops must be irrigated most of the year. Afghanistan,
and Sudan apply an estimated 99 percent of all the water they use to
agriculture.
The
area of irrigated land worldwide nearly doubled in the first half of this
century to meet the needs of a growing population that was developing
economically and consuming more food per capita. Land under irrigation more than
doubled again between 1950 and 1990. 8 Only in recent years has the
growth of irrigation slowed, reflecting the challenge of finding new sites for
dams and reservoirs and of squeezing more water out of already overpumped
aquifers. In California and the southwestern United States water is becoming so
valuable that farmers are selling their land--and the accompanying water
rights--to ballooning metropolitan areas with huge demand. A few countries, such
as Malta and Botswana, have opted to rely on imported food in part to save
water. This reduces the need for irrigation water, but at the risk of limiting
options if imported food becomes expensive.
Domestic
water use--including drinking, food preparation, washing, cleaning, gardens and
service industries such as restaurants and laundromats--accounts for only a
small portion of total use in most countries. The amount of water people apply
to household purposes tends to increase with rising standards of living, and
variations in domestic water use are substantial. In the United States, each
individual typically uses more than 700 liters each day, or 185 gallons, for
domestic tasks. In Senegal, the average individual uses just one twentieth of
that--29 liters, or 7.6 gallons--to meet household needs. 3 Domestic
needs account for a greater share of overall use in countries, rich or poor,
that have little agriculture or industry. In both Kuwait and Zambia, nearly two
out of every three liters of water are used in households.
Industry,
a category that includes energy production, uses water for cooling, processing,
cleaning and removing industrial wastes. Nuclear and fossil-fueled power plants
are the single largest industrial users, applying staggering amounts of water to
the job of cooling. 9 While most of the water used for industrial
purposes is returned to the water cycle, it is often contaminated by chemicals
and heavy metals, or its temperature is increased to the detriment of water
ecosystems. Industrial use varies from less than 5 percent of withdrawals in
dozens of developing countries to as much as 85 percent in Belgium and Finland.
Only in Europe, where reliance on irrigation is relatively low, does industrial
water use equal the sum of water applied to agriculture and domestic uses. The
proportion of water used for industrial purposes is often seen as an indicator
of economic development.