PHOENIX (AP) - The seven states that rely on the Colorado River for drinking water are looking beyond traditional approaches as they try to further stretch a supply already stressed by population growth and an ongoing drought.

In a letter to Interior Secretary Gale Norton, representatives of the seven states - Arizona, New Mexico, Colorado, Wyoming, Utah, Nevada and California - outlined proposals for dealing with or averting shortages.

The focus is on three areas, including augmenting the river's flow, operating the river more efficiently by getting more usable water from the existing flow and finding better ways to manage the overall system.

Though it sounds simple, adding to the river's flow has been part of the West's long-range plan for the Colorado since at least 1968.

The idea was included in the legislation that authorized the Central Arizona Project canal system, which delivers Colorado River water to Phoenix, Tucson and Pinal County.

That part of the law gathered dust because few of the states were using their full shares of the river for so long. But this year, Arizona and other river states concluded they were running out of options to avert shortages.

Among the possible sources of new water, the easiest and cheapest to try is cloud seeding: spewing silver iodide, or dry ice, particles into a storm to induce more rain or snow. The technology is more than 60 years old and scientists say it works, as long there are clouds and moisture to tap.

The best hope for increasing runoff on the Colorado is to seed clouds over the river's headwaters in the high Rocky Mountains of Colorado.

Arlen Huggins, a research scientist at the Desert Research Institute in Reno, said cloud seeding is most effective in winter and at high elevations.

"That's where most of the water is wrapped up for stream flow," Huggins said. "Water supplies out here are very closely tied to how much snow you get in the winter."

The basic seeding technology is little changed since it was discovered in the late 1940s, but Huggins said scientists have learned much about when and where to inject the particles and which storms are most likely to produce extra rain or snow.

A cloud-seeding operation can increase moisture from a storm up to 10 percent in specific areas, though the results vary over a broader river or drainage basin.

Utah, which runs one of the oldest and largest cloud-seeding projects in the West, estimates it has increased runoff an average of 13 percent a year. This year, the state and its private partners will spend more than $400,000 on cloud seeding across four drainage areas.

Colorado, New Mexico and Wyoming have also experimented with cloud seeding and operate projects on a smaller scale. Arizona has studied cloud seeding over the years.

Larry Dozier, deputy general manager of the Central Arizona Project and one of the people working on the seven-state proposal, said cloud seeding is only a stopgap solution and not one that could cover all shortages in dry years.

He wants the states to explore even more innovative ideas, such as building a water desalination plant on the Gulf of California.