The distribution of water resources around the globe is highly unequal, even at the continental level. Asia has more than 60 percent of the world population but only 36 percent of river runoff (much of it confined to the short monsoon season). South America, meanwhile, has just 6 percent of the global population but 26 percent of runoff. Canada has more than 30 times as much water available to each of its citizens as China.

Many of the world’s largest river catchments run through thinly populated regions. These include the Amazon (15 percent of global runoff but 0.4 percent of global population) and the Zaire-Congo that flow into the Atlantic Ocean, and the great rivers of northern Canada and Siberia that flow into the Arctic Ocean. Meanwhile, many countries with high population density or growth rates, such as Pakistan and Egypt, are in hot, water-stressed regions where crops require irrigation¹.

Water withdrawals from rivers and underground reserves have grown by 2.5 to 3 percent annually since 1940, significantly ahead of population growth. Already, little of the water in some of the world’s major rivers reaches the sea, including the Colorado in the United States, the Nile in Egypt and, for much of the year, the Yellow River in China².

Water tables are falling on every continent. Shortages are having an increasing effect on global grain markets, as arid countries that rely on irrigation for crop production are switching to food imports. As a result, North Africa and the Middle East were the fastest growing import markets for grain in the 1990s. The World Bank warns that freshwater is likely to become one of the major factors limiting economic development³.

At the start of the 21st century, 49 countries with around 35 percent of the world population were believed to have less than 2 000 cubic meters of renewable freshwater available per capita per year⁴, implying water scarcity or chronic shortage. Major nations in the list include India, Ethiopia, Nigeria and Kenya. Northern China also faces major shortages.

The crisis is likely to be worsened by the deteriorating quality of water, polluted by industrial wastes and sewage discharges, and spreading water-related diseases such as cholera and schistosomiasis. In addition, many regions watered by international rivers have yet to draw up agreements to share supplies. On the River Euphrates, Turkey has built several large dams without prior agreement with downstream neighbors Syria and Iraq. On the River Nile, Egypt uses 85 percent of the river’s flow but has no agreement with potentially major upstream users such as Ethiopia. Unresolved disputes over riparian rights also fester within many countries.

More than 60 percent of the water used in the world each year is diverted for irrigating crops. Egypt, which must irrigate all its crops, uses more than five times as much water per capita as Switzerland. In Asia, which has two thirds of the world’s irrigated land, 85 percent of water goes for irrigation. A worldwide doubling in the area under irrigation to more than 260 million hectares underpinned the “green revolution” that kept the world fed in the late 20th century. Almost 40 percent of the global food harvest now comes from the 17 percent of the world’s croplands that are made productive in this way⁵.

In some countries there is an increasing reliance on pumping underground water, often at rates that rainfall cannot replenish. Libya, for instance, by pumping “fossil” water from deep beneath the Sahara desert, uses seven times more water annually for irrigation than it receives in rainfall. India is pumping water at twice the recharge rate, causing some water tables to fall by between 1 and 3 meters a year. The country’s grain production could fall by 25 percent if it gave up groundwater “mining”⁶.

Most irrigation schemes around the world are extremely inefficient. Typically, less than half
the water reaches crop roots. Much of it is misdirected or evaporates. Meanwhile, over-irrigation combined with inadequate drainage is causing an accumulation of salt that is reducing yields in many of the areas under irrigation. Sometimes there are major ecological impacts. Irrigation projects developed by the former Soviet Union in Central Asia to grow cotton have dramatically emptied the Aral Sea, destroying fisheries, depopulating large areas and causing epidemics of disease.