In the arid Southwest, water in the reservoir is like having money in the bank - and it may eventually be worth every bit as much.
States in this region increasingly are "banking" their share of water from the Colorado River and its main tributaries in the hope that someday soon they will sell and trade stored water as a commodity.
Such a move would represent a fundamental shift in how Western states control and pay for the region's most precious resource - with implications for everyone from California broccoli growers to Las Vegas greenskeepers.
Indeed, Arizona, the emerging pioneer of water banking, has already touched off a new skirmish in the century-old war over water in the West - the lifeblood of the high desert region.
Arizona's decision to store more Colorado River water than ever before "sends a very loud wake-up call to California that they need to find alternate sources of water," says Rita Pearson, director of the Arizona Department of Water Resources.
The action will deprive southern California - the user furthest downstream - of water it is used to getting. By right the water belongs to Arizona, but until now the state has let its unused portion run to the west - primarily into the fields of California farmers such as Bob Bornt.
A third-generation grower whose family works 1,000 acres in the Imperial Valley outside Holtville, Calif., Mr. Bornt says Arizona's action probably won't have an immediate effect on the farm. But in the long run, the family may need to buy additional water-conserving equipment - a cost that would ultimately be passed on to consumers in higher prices for his vegetables.
Against this backdrop, Utah has recently expanded the water-storage capacity of its major reservoir by 200 percent. The Jordanelle Reservoir is a shrine to the importance of water in the West. Looking more like an Athenian temple than a cavern for water collection, the reservoir, buttressed by 730 35-foot columns, is intended to help satisfy the water needs of 500,000 customers, says David Ovard of the Salt Lake County Water Conservancy District.
But Utah also embraces the idea of selling its unused water. Ted Stewart, executive director of the Utah Department of Natural Resources, says the state's Colorado River water supply will far exceed Utah's needs.
"If we could lease [the unused portion] and get compensation for it, it would be far better than to let it flow downriver and let other states get it for free," he says.
The US Interior Department - with jurisdiction over the Colorado River's massive interstate network of dams, reservoirs, and aqueducts - will decide on a case-by-case basis whether to allow one state to sell its water to another.
Meanwhile, US Interior Secretary Bruce Babbitt, a former Arizona governor, says Arizona's water bank - actually several underground aquifers - could help other arid states. Arizona could hold not only its own unused allotment, but also that of Nevada and California. Those states could then draw upon that supply in times of need.
But agreement is by no means universal among upper-basin states (Wyoming, Utah, Colorado, and New Mexico) to sell their water to those in the lower basin.
Philip Mutz, New Mexico's upper Colorado River commissioner, says his state is wary of such transfers, concerned that they might crimp New Mexico's economic development. "Once the water is transferred out of the upper basin, you don't know how to get it back."
Annual Allotment of Colorado River Water
California 4.40 million acre feet*
Wyoming 840. thousand acre feet
New Mexico 675.
* An acre foot is 43,560 cubic feet - or the amount of water that covers one acre to a depth of one foot.
Source: Department of Interior