ULYSSES, Kan. -- In recent weeks, this oil-and-gas town of 6,000 has been looking into buying water -- perhaps $190,000 worth of the stuff.

The Ogallala aquifer, the vast underground pool that feeds faucets across the Great Plains, is running low, forcing farmers and towns to find other sources of water and pay dearly for it, too.

"Out here, water is like gold," Mayor Ed Wiltse said as he ran his hands over a chart of the town's faltering wells. "Without it, we perish."

The Ogallala aquifer is the world's largest underground water system, irrigating one-third of the nation's corn crops and providing drinking water to Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas and Wyoming. It contains enough water to cover the entire United States to a depth of 1 1/2 feet.

But because of heavy usage, some water experts have pronounced it one of the fastest-disappearing aquifers in the world.

Now, after generations in which water from the Ogallala was treated as if it were an inexhaustible resource, farmers, cities, states and the federal government are talking seriously about conservation.

In some places across the country, the aquifer is flush with water. Near Nebraska's Platte River, for instance, streams quickly recharge its underground channels. But Kansas hydrologists estimate that around Ulysses, the aquifer may have only 25 years left if current usage continues.

Since the 1940s, Ulysses' wells have drawn from the Ogallala aquifer. But Ulysses sits in a stretch of the Corn Belt where the water table has dropped 25 feet in the past decade. Once-wild rivers have turned to gravel, and streams stopped running years ago. And after years of drought, it has been a long time since anyone thought the sky might water the crops.

Some farmers in Ulysses and beyond have started switching from corn to cotton, which needs less water. But for drinking water and water for industry, towns have little choice but to spend millions to move water from miles away.

"We've just gone through a four-year drought," Wiltse said. "So now we're having to go further out from the city to purchase water rights. This time, we're not only paying to buy more water, but we'll be paying for underground water pipelines and booster pumps."

Similarly, the city of Lubbock, Texas, began buying up new water rights last year. The municipal water authority will spend $100 million to supply the town with water for the next century.

"This ain't the time to play politics," said Lubbock City Councilman Gary Boren. "It's one of those things that if you don't have it, you'll pay any price to get it."

After nearly a century of state policy that doled out water rights to farmers almost indiscriminately, Kansas has virtually banned any new uses of water along the state's western edge. A group of concerned growers in Thomas County, near the Colorado line, is considering an across-the-board 10 percent reduction in water use. And last month, Gov. Kathleen Sebelius proposed to pay farmers to stop watering their crops.

"Once that water is used, it's not going to come back," said hydrologist Brownie Wilson, who monitors water declines at the University of Kansas in Lawrence. "Whether it's better to use it now or save it for tomorrow is where you get the debate."

The federal government is also trying to take action. This year's agriculture appropriations bill acknowledges the aquifer could go dry within two decades and calls for federal conservation efforts.

"There's an old saying that whiskey's for drinking and water's for fighting," said Sen. Sam Brownback, R-Kan. "Water is the lifeblood of this region. There's no question that it is our biggest policy question."

However, the National Corn Growers Association and the American Farm Bureau oppose federal regulation of groundwater, arguing that water rights are a state issue.