If you have a detailed globe or atlas in your house, it almost certainly has a serious error in it. The error is that the Fen River, shown on maps as the principal river in China's Shanxi Province, no longer exists.

What happened to it?

And why does it matter to us, here on the other side of the world? To answer the first question first, what happened to the Fen is that it dried up. The reason, according to Lester Brown, president of Worldwatch Institute, is that the people in Shanxi Province, and in much of China as well, are using water faster than the water is being replaced.

"The northern half of China," he warns, "is literally drying out. The water table under Shanxi's capital city, Taiyuan, has dropped to 300 feet or more below the surface.

"When the water table falls," he continues, "at first, the streams and springs go dry. Eventually the rivers also stop flowing."

Of China's 617 major cities, 300 today face water shortages. Many of the cities respond to the water shortage by diverting water from agriculture.

The reason for this diversion is economic, and the mathematics of it are stark. A farmer can produce $200 worth of wheat with a thousand tons of water. That same thousand tons of water used in industry will yield about $14,000, or 70 times as much.

The problem of water scarcity is serious now, but it's getting worse. "China's population," points out Brown, "is still projected to grow by another 300 million in the next 30 years. During that time it will go from 1.2 billion to 1.5 billion.

"Even if China holds the line on family size," he goes on to say, "they will still add another United States to their current population."

China's water scarcity will have serious repercussions for the United States. As China continues to divert water away from agriculture, it will need to import more grain.

It can do this since it's currently running a $40 billion a year trade surplus. In theory, China could afford to buy all the grain that we export.

At first sight, this might look like a windfall for us, or at least for the American grain farmers. But a sharp increase in world grain prices has a darker side.

In areas where people already spend most of their income on food, a rise in grain prices isn't an annoyance; it's a matter of life and death. A number of low income countries are heavily dependent on imported grain as it is, and paying for that grain is already problematic.

What happens when the price of grain rises? The answer will be serious for such countries as: the Philippines, Indonesia, Pakistan, India, Egypt, Ethiopia, Morocco and Mexico.

This concerns the United States for humanitarian reasons. It also concerns us for political reasons, since shortages of food mean political instability, refuges, and possibly wars.

The problem is reasonably clear, but the solutions are not. Brown and the Worldwatch Institute hope that the U.S. and China will share technology on ways of conserving water.

But the bigger problem, according to Brown, is the population explosion. The larger the world population, the worse the problems stemming from water shortages. He's puzzled that so few leaders address the problem.

"I sometimes wonder," he says, "what the next generation will think of us when they realize that our failure to act has caused them so many problems."