WASHINGTON - The director of the Arizona Municipal Water Users Association told a Senate subcommittee this week that there is no "silver bullet" to the problem of rising demand for water from the Colorado River.

Kathleen Ferris pointed to Arizona's years of successful water management policies that have kept water use at virtually the same level since 1957, despite an exploding population. But while conservation and reuse are essential, Ferris said other measures need to be taken, such as the augmentation of supplies.

"We have to expand our thinking," Ferris told a subcommittee of the Senate Energy and Natural Resources Committee.

She was one of several government, tribal and expert witnesses who appeared before the Subcommittee on Water and Power to discuss the Bureau of Reclamation's December study on water supply and demand in the Colorado River Basin.

That study laid out challenges for the river, which provides drinking water to nearly 40 million people, generates 4,200 megawatts of hydropower, delivers water for farm irrigation and provides recreational opportunities that help drive tourism in the region.

The study said the river is facing demand from growing populations and is undergoing a drought that has put flows at their lowest levels in at least 100 years - and possibly the lowest in 1,200 years. It projected that in 50 years, demand could outstrip supply of river water by about 3.2 million acre-feet per year.

The bureau does not make specific recommendations, instead outlining the threats and "the range of solutions … that may be considered to resolve those imbalances," said bureau Commissioner Michael Connor in his testimony.

Taylor Hawes, the director of the Colorado River Program at the Nature Conservancy, told the hearing that states in the basin are heading into uncharted territory.

Besides the environmental issues, Hawes said the Colorado also needs to be preserved because of the recreation it provides and the jobs that come with that.