In 1893, John Wesley Powell of Grand Canyon fame, Director of the US Geological Survey, addressed an irrigation conference in Los Angeles about water in the American West. He flatly stated that there was insufficient water in the American West to support widespread irrigation agriculture. Powell was shouted down, forced by hostile interests in Congress to resign from the Geological Survey. But history has shown he was right, for our reckless consumption has taken us far beyond the point of sustainability.

The Colorado River offers a sobering portrait of the western future. Data from the past presents a daunting picture of what may lie ahead. Colorado Plateau tree-ring records reveal severe droughts between 1564 and 1600 and again from 1868 to 1892. Further back in time, there was a prolonged and severe dry cycle between 1139 and 1154. Elsewhere, tree-stump rings in Owens Lake show a major drought from before 910 to 1100 and another long, intensely dry spell from before 1250 to about 1350. Until the last century, the West's population was small enough to swing with the punches. By 2050, millions more people will compete for Colorado water. If present trends continue, rising temperatures will reduce the flow of the already drought-depleted river by a further 10%.

No question, our grandchildren and great grandchildren will live in a very different hydrological world. Quite apart from renegotiating the now-obsolete Colorado River Compact, we will have to break the habits of our lifetimes and use water very differently. If, for example, we reduced agricultural allocations and the amount of city water going to landscaping from 50% to 5%, we would save nearly 20% of the annual flow of the Colorado River alone.

Groundwater is also vanishing further to the east, from Colorado and New Mexico to Texas, Oklahoma, and Nebraska, where the vast Ogallala aquifer under the Great Plains supports hundreds of communities, also large cities and major agricultural and mining activities. The Ogallala supplies about a third of the nation's groundwater used for irrigation. US Geological Survey experts have calculated that irrigation alone sucked about 21 million acre feet (260 cubic kilometers) of water from the Ogallala in 2000, a figure slightly larger than the historic annual discharge rate of the Colorado River. Some hydrologists believe that the aquifer will dry up in about 25 years.

Even without sustained warming and mounting aridity, much of the United States lives on borrowed time. Climatic changes are already raising the hydrological stakes, which raises another disturbing question. How much longer will this country be able to provide surplus food to other hungry parts of the world as it has done in the past? In the foreseeable future, the water supplies that feed crops will be potentially more valuable than the thirsty cotton and rice they irrigate in so many arid environments.

The problem is global, for 70% of our withdrawals from this fixed water "bank account" goes to agriculture, this in the face of ever-greater domestic and industrial usage. Water tables are falling in many parts of the world, among them China, India, and the United States. The Himalayan glaciers will shrink massively in the next century, reducing natural water storage in the mountains. The shortfalls will have to come from groundwater and surface storage. Many great rivers have drastically diminished flows. Bangladesh is suffering from diversion of Ganges River water and increased salinization. Underground aquifers in many places are shrinking so rapidly that NASA satellites are detecting changes in the earth's gravity. The Water Resources Group has estimated that India alone may face a 50% lag in water availability relative to demand by 2030. Sixty years ago, the world's population was about 1.25 billion people; few people, even in arid lands, worried about water supplies. Then came the Green Revolution with its new, high-yielding crops, which depend on fertilizers and a great deal more irrigated farming. Global populations skyrocketed--to nearly 7 billion by 2009 and a projected 9 billion by 2050. By the same year, the 500 million people living in areas chronically short of water in the year 2000 will have risen by 45% to 4 billion. A billion of us currently go hungry because there is not enough water for them to grow food. Much of the world's water is still unpriced, but is becoming the most valuable commodity in the world. No wonder are quietly buying water rights where they can.

An endless flow of water links every part of our existence. Yet, for all our efforts to channel and control it, water governs itself and often defies capture. This means that we have to conserve every drop we can, even if it means major changes in our ways of life. At present we're largely in denial of this reality.

