Our murky freshwater future.

Global warming is burning off the world's water. Why aren't we doing more about it?

RESPONDING TO A LOOMING CRISIS IN THE national supply of things to worry about, government hydrologists have tapped into a completely new domestic source of anxiety: water. It seems that a natural resource most folks find as dependable as, well, tap water is likely to prove alarmingly hard to find in the near future.

The water crisis only threatens the developed world; it is already a reality in less-affluent parts of the planet. One out of the earth's five inhabitants lacks access to clean drinking water. Nearly 3 billion live without proper sanitation, and more than 5 million people die each year of easily preventable waterborne diseases such as diarrhea, dysentery, and cholera.

At about 2.5 percent of all water (and two-thirds of that "stored" out of reach in glaciers and ice caps), the supply of freshwater can never change. What can change is who gets to turn the spigot.

"Nations go to war over oil, but there are substitutes for oil," Senator Paul Simon writes in an op-ed piece in the New York Times. "How much more intractable might wars be that are fought over water, an ever scarcer commodity for which there is no substitute?" A CIA analysis agrees that water may become a fought-over resource in the world's arid regions.

Combat in the United States may remain only political, but U.S. freshwater supplies may also reach critical levels in the coming generation. Studies warn that wells and marshes could dry up, aquifers collapse, and lake levels decline. U.S. farmers, suburban and city planners, and industrialists will have to war over their share of America's waters. The losers in this conflict most likely will be wetlands and wildlife.

The drying up of America is not news to folks in the Southwest who already watch the Colorado River trickle down to a pathetic, toxin-heavy puddle a few hundred miles short of the Sea of Cortes. To people living in the Great Lakes region, the idea of a water crisis may be harder to swallow, but lake levels have declined for four years straight while wells and wetlands in surrounding communities have been drying up.

The growing demands of agriculture and expanding cities contribute to the crisis, and suburban sprawl is a significant factor. As more wetlands and open lands are paved over, underground aquifers are unable to become recharged by rainfall. But, according to hydrologists, global warming may be the largest contributor to water scarcity as surface water burns off before it can restore water reserves. Naturally, global warming skeptics will dismiss this projected water crisis, pretty much as they dismiss the gamut of ecological and geopolitical crises that have been conjectured around global warming. Their optimism, however reassuring, remains puzzling.

It has been a standard Yankee ethic to prepare for the worst and hope for the best. Not too long ago a beloved president got himself reelected partly on the strength of a snazzy commercial campaign that depicted a big old bear prowling through the woods. The ad noted that some people could see the bear and some couldn't and that the bear may or may not be dangerous but argued either way it was worth being prepared for the bear, "if there is a bear."

That's not bad advice for contemporary policy makers as they confront the dual threats of water scarcity and global warming. Why demand absolute scientific certainty about the existence of global warming? Why not acknowledge that 150 years of massive carbon burning must have had some effect on the planet's pulmonary system? Why not accept that research indicating warming is already underway may be accurate? We were willing to "invest" billions on defense spending to chase off that other bear and deter the speculative threat of an enemy who at least could be reasoned with.

Not like this enemy. The "bear" that is global warming cannot be bargained with, it cannot be persuaded to act responsibly, it can only be prepared for.

As stewards of creation, we must make good, if difficult, choices about water conservation and allocation in the future. But first we have to confront that bear in the woods. It can't be chased or wished away, and if it's thirsty when we run into it, I hope we'll at least be able to offer it a glass of water.

By KEVIN CLARKE, managing editor of online products at Claretian Publications in Chicago.