1. Nor any drop to drink

2. A global shortage

3. Bright signs

4. Supply and demand

5.Global warming

A center-pivot irrigator has a long horizontal pipe. The inner end pivots, and the outer end is on wheels. As the irrigator pivots, it creates a circular field.
Courtesy Mitchel Resnick and Brian Silverman, MIT

As we in water-rich countries take our daily showers, water the lawn or laze about in the pool, it's easy to forget that fresh water is a life-or-death issue in many parts of the world.

Of a population of roughly 6.1 billion, more than 1 billion lack access to potable water. The World Health Organization says that at any time, up to half of humanity has one of the six main diseases -- diarrhea, schistosomiasis, or trachoma, or infestation with ascaris, guinea worm, or hookworm -- associated with poor drinking water and inadequate sanitation. About 5 million people die each year from poor drinking water, poor sanitation, or a dirty home environment -- often resulting from water shortage (see "Tackling the Big Three" in the bibliography).

Parched places
One glance at the map tells you that water is shortest in equatorial countries, often where populations are rising. (Population data below from Population Reference Bureau).

China, with 1.26 billion people, is "the one area worrying most people most of the time," says Marq de Villiers, author of the recently published "Water " (see bibliography). In dry Northern China, he says, "the water table is dropping one meter per year due to overpumping, and the Chinese admit that 300 cities are running short. They are diverting water from agriculture and farmers are going out of business." Some Chinese rivers are so polluted with heavy metals that they can't be used for irrigation, he adds.

"They're disgraceful, unusable, industrial sewers," says de Villiers. As farmers go out of business, China will have to import more food.

In India, home to 1.002 billion people, key aquifers are being overpumped, and the soil is growing saltier through contamination with irrigation water. Irrigation was a key to increasing food production in India during the green revolution, and as the population surges toward a projected 1.363 billion in 2025, its crops will continue to depend on clean water and clean soil.

Israel (population 6.2 million), invented many water-conserving technologies, but water withdrawals still exceed resupply. Overpumping of aquifers along the coast is allowing seawater to pollute drinking water. Like neighboring Jordan, Israel is largely dependent on the Jordan River for fresh water.

Water Fight
Egypt, whose population of 68 million may reach 97 million by 2025, gets essentially no rainfall. All agriculture is irrigated by seasonal floods from the Nile River, and from water stored behind the Aswan High Dam. Any interference with water flow by Sudan or Ethiopia could starve Egypt.

"The Nile is one I worry about," says Sandra Postel, director of the Global Water Policy Project. Egypt, she says, is militarily powerful but vulnerable. "The hydropolitics might favor some military action, because Egypt is so heavily dependent on the Nile, it's already virtually tapping out the supply, and Ethiopia is now getting interested in developing the headwaters."

When a World Bank official suggested several years ago that water wars are not far off, he might have had Egypt on his mind -- or Turkey, Syria and Iraq, another trio of Middle-Eastern states that are locked in an uncomfortable embrace over water.

The Tigris and Euphrates Rivers both rise in Turkey and flow unimpeded to Syria and Iraq, where they provide the bulk of irrigation water needed in the arid climate. Turkey has proposed a series of dams that would reduce river flow. That causes alarm downstream.

A working river
International water politics play a role in the Southwestern United States, where the Colorado River is shared by many states before its dregs trickle into Mexico. All along the river, water is diverted for irrigation and urban water -- with Arizona and California the biggest users. Because Mexico uses the dribble of water that reaches it for irrigation, virtually nothing reaches the river's once-fertile -- and now parched and polluted -- delta on the Sea of Cortez.

The Colorado may be completely allocated, but the Southwest continues booming. According to one estimate, five of the 10 fastest-growing U.S. states are in the river's drainage. The water the newcomers drink is likely to come from farmers who now receive subsidized river water.

The rivers we've mentioned are some of the 200 and 300 major lakes and rivers that transcend national boundaries. The list includes such major items as the Nile, the Amur River between Russia and parched northern China, the Niger in Africa, and the Mekong, Indus and Ganges in Asia.

Can't anyone get along?