A number of developed water-short countries currently face tensions over water, including Belgium, the United Kingdom, Poland, Singapore, and the US (69). In southern Britain, for instance, urban demand for water is growing so fast that it is outpacing the capacity of rivers and aquifers to supply it during the drier summer months. In the western US, farmers who want more irrigation water for their crops face off against fast-growing urban areas that demand more water for households and other municipal uses (138).

India's states have become embroiled in disputes over water rights and over dams that might provide more water for one state but at the expense of another. "Water disputes, if not attended to, will become a major headache for the stability of Indian society," says Mohan Katarki, a lawyer representing Karnataka state in a water dispute with Andhra Pradesh (129). These two states are arguing in court over the height of a dam on the Krishna River, which could affect the amount of water available for use by both states.

China already is practicing what some water experts call the "zero sum game of water management" (138). The zero sum game—when authorities increase water supply to one user by taking it away from another—is played both between competing areas of the country and between competing types of use, as when cities compete with farmers. China's Yellow River is a classic case of the zero sum game. The river is so oversubscribed that, for an average of 70 days a year for the past decade, its waters have dried up before reaching the Bohai Sea. In 1995 the dry period lasted for 122 days. In 1996, one of the few years when there was enough water for farming villages near the river's mouth to feed their crops, the government authorities ordered them not to touch a drop. All of the water flowing by their parched fields was destined for use by a state-run oil field farther downstream (172).

Also, to meet urban needs, the government of China is planning a huge aqueduct that will carry water from the Danjiangkou Reservoir in Henan Province to Beijing, across 1,300 kilometers of heavily farmed land—land that also needs the water for food production (87, 173).

If China diverts too much water from agricultural uses, grain production is likely to suffer, probably forcing China to import more grain. Other grain-producing countries, however, have little potential to boost exports, warns the Worldwatch Institute. In the US and Europe, for example, increases in agricultural productivity are just keeping up with population increases. Australia and Canada depend on dryland farming and are constrained by limited rainfall. Thus "China's water scarcity could soon become the world's grain scarcity," the Worldwatch Institute predicts (15). Increasing demand for grain in China could raise prices on the world market beyond the reach of some poor countries.

Regional conflicts. In nearly all water-short areas the threat of regional conflicts over limited water supplies is emerging as a serious issue (58, 120). In Africa, for example, about 50 rivers are each shared by two or more countries. In particular, access to water from the Nile, Zambezi, Niger, and Volta river basins has the potential to ignite conflicts (197).

In Central Asia the Aral Sea Basin is beset by international conflicts over water. Turkmenistan, Uzbekistan, Kazakstan, Kyrgyzstan, and Tajikistan all depend for their survival on the waters of the Amu Darya and Syr Darya rivers. The flows of both rivers are almost wholly diverted to feed water-intensive crops such as cotton and rice. In most years only a trickle reaches the Aral Sea (89, 164). As demand for this water grows, the countries are increasingly at odds over its division, with all five Central Asian republics demanding a greater share (40, 89). Disputes are growing between Kyrgyz and Uzbeks over water and land in the fertile Fergana Valley; between Kyrgyz and Tajiks over the allocation of irrigation water from the Syr Darya; and between Turkmens and Uzbeks over the distribution of irrigation water from the Amu Darya (138).

In the US, the Colorado River, which flows through the southwestern part of the country, has fed irrigated agriculture and enabled the explosive growth of desert cities. Now, however, demands on the river's water supply for irrigation and urban use have become so great that the river no longer reaches its mouth in Mexico's Gulf of California. Instead, its waters trickle out somewhere in the desert south of the US- Mexican border (140). The river's premature disappearance has been a source of bickering between the US and Mexico.