Southern Nevada at long last is using all of the state's share of Colorado River water. Does this mean the Las Vegas Valley is out of water? Not necessarily. Not yet.

What it does mean is that local water agencies might have to dip into emergency reserves within the next year or two to make it through the ongoing drought. Meanwhile, they are calling for conservation and are working to develop alternative supplies. Yet many of these alternative supplies aren't permanent sources, a cause for concern among Arizona officials as well as environmentalists.

Projections from 1999 show that Nevada was not expected to use its full share of river water before 2007, by which time it would have other sources in hand to more easily accommodate growth. Growth, however, has consistently outpaced projections. According to the latest estimates, Southern Nevada by the end of the year will have used 320,000 acre-feet of river water, 20,000 acre-feet more than its allowed annual apportionment. The state probably will need up to 700,000 acre-feet annually within the next 20 years if people continue to move here at the current rate of about 5,000 people per month.

An acre-foot, 326,000 gallons, is enough to meet the needs of a Las Vegas family of four for a year. These projections are staggering to critics, who say local officials should limit growth until Southern Nevada has a firm water supply to sustain such demand. Southern Nevada Water Authority officials say they are confident new river surplus guidelines meant to help California reduce its dependence on the Colorado will provide a temporary supply to Nevada for the next 15 years. They say those 15 years will provide enough time to develop alternative water sources.

The new guidelines allow Nevada to take more than its allocation of river water if snowmelt from the Rocky Mountains produces above-average flows. But the availability of surplus water might be in jeopardy as the four-year drought on the upper Colorado River takes its toll. The U.S. Bureau of Reclamation estimates the river's flow this year is 70 percent below average. Even so the secretary of the Interior has declared a surplus on the river based on the surface elevation of Lake Mead. But because those elevations are dropping, some restrictions have been placed on how the surplus water can be used.

Lake Mead's elevation, which this year has been dropping at a rate of about a foot per week, on Friday was at 1,159 feet. If the elevation falls below 1,145 feet, the amount of water Nevada could take above its basic annual apportionment would have to be cut in half. "There is no projection right now of how much, if any, surplus will be declared for next year," said Robert Walsh, a spokesman for the bureau. The bureau projects the lake could hit the critical 1,145-foot elevation by next May. This means that within the next year or two, water authorities might have to dip into the state's groundwater reserves for at least 10,000 acre-feet, unless the community starts taking conservation more seriously, said Pat Mulroy, general manager of the Southern Nevada Water Authority.

"If we want to put ourselves in the best possible position for the worst-case scenario, this would be the year to get serious about our water use and habits," Mulroy said. "People need to know how critically important conservation is."

George Caan, executive director of the Colorado River Commission in Nevada, said the state's water worries stem from the explosive population growth, which no one anticipated when water rights to the Colorado River were first decided in the early 1900s. "This was a train stop," Caan said. "No one ever expected Nevada to fully utilize its apportionment of the river because no one ever expected this community to grow as it has."

Of the seven states sharing the river's flows, Nevada's apportionment of 300,000 acre-feet is the most meager. In contrast, California is entitled to 4.4 million acre-feet, and Arizona to 2.8 million acre-feet. California for years has used far more than its share, depending largely on unused apportionments from Nevada and Arizona. Arizona does not yet need its full apportionment, but now stores some of its unused share underground for future use.

Mulroy said that up until this year, Nevada has been able to pump its unused apportionment and some surplus water for an artificial groundwater recharge program. The program allows local water agencies to store water in an aquifer for future use. Since 1987, the water authority has banked about 250,000 acre-feet, which could be used today if necessary, Mulroy said.

But because of the drought, she said the state won't pump water for storage until the drought subsides. Any water Nevada pumps from the river above its 300,000 acre-feet apportionment must be restricted to direct domestic needs, including residential and industrial uses. "The only way we could bank this year is if through some miracle, the community conserves enough to keep us below the 300,000 acre-feet apportionment," she said. Although water officials say conservation is key to ensuring the valley maintains a healthy water supply, critics say it's not reliable.

"Voluntary conservation measures are not the answer," said David Hogan, rivers program coordinator for the Center for Biological Diversity, an Arizona-based environmental group. "Ending unsustainable growth is the solution, and that includes stopping ever-greater developments that contribute to urban sprawl." Clark County Commissioner Myrna Williams, agreed that growth poses a difficult dilemma for lawmakers, who also deal with water issues. "Growth plays a part in our water issues, but I don't know how we can stop people from moving here," said Williams, who also is board president for the Las Vegas Valley Water District. "It's a double-edged sword. We need it for our economy. We need to take care of the population we've got, and we've got to use our water judiciously."

Mulroy said officials know local residents have a long way to go in making conservation a real part of desert living. But they have made strides to improve their water-use habits. Local municipalities, for example, have adopted ordinances regulating outdoor watering in the summer months, and water purveyors are beginning to fine chronic water wasters. Even so, highly publicized conservation campaigns have failed to generate the level of conservation water officials had desired. The Southern Nevada Water Authority has missed its conservation goals for the past three years. In 2001 alone, the authority estimates the public wasted 30 billion gallons just by over-watering lawns and landscapes.

Kay Brothers, resource director for the Southern Nevada Water Authority, said that if the federal government calls for a reduction in the use of surplus river water, saving the gallons of wasted water could be enough to cushion the blow, at least for the coming year or two. The water authority on Thursday approved spending $200,000 on an advertising campaign to increase public awareness and urge communitywide conservation. With the drought and ever-increasing demand in mind, the water authority has pointed its water wand toward Arizona, which still isn't using its full allocation.

Water authority officials in 1993 participated in a demonstration project, which stored 50,000 acre-feet in Arizona for use by Nevada. In 1996, the Arizona legislature created the Arizona Water Banking Authority to store or "bank" the state's unused Colorado River water apportionment to offset possible future shortages on the Colorado River, reduce overdraft of Arizona's groundwater basins and help settle Indian water-rights claims. The water authority on Thursday approved agreements with the federal government, Arizona and the Colorado River Commission to move forward with the project, which could store up to 1.2 million acre-feet for Nevada over the next 20 years.

But Arizona water experts say the deal won't be the silver bullet for Nevada, given the drought and ongoing growth. "Over the next 10 years, Nevada must find alternative sources of water," said Bob Barrett, a spokesman for the Central Arizona Project, which runs the water banking operations there. "We are not your long-term solution." He said growth in Arizona is rapidly increasing demand on the river. As Arizona's demand increases, the availability of water for Nevada decreases.

Larry Paulson, a retired biologist from the University of Nevada, Las Vegas, who has long followed water issues along the Colorado, said the state is living dangerously. He said allowing growth to continue at the current rate without a guaranteed water supply to sustain the valley could leave Nevadans in a bind sooner than they think. "We're flirting with disaster," he said. "All the options I've heard the water authority is looking at sound iffy. They may or may not be enough to sustain Southern Nevada long into the future."

But Brothers says she is confident existing resources will carry Nevada at least into the next 50 years. "We're not going to run out of water because we continue to plan," Brothers said. She said conservation, the guidelines regarding surplus use, and groundwater stored in the valley's own aquifer will be enough to sustain growth at its current rate until 2016. The authority's long-term plan outlines a water resource strategy for meeting the area's needs beyond 2016. Southern Nevada's continued growth will depend on transfers from the Arizona groundwater bank and the use of up to 40,000 acre-feet from Nevada's own groundwater. Also, the authority has rights to 5,600 acre-feet per year from the Muddy River, 113,000 acre-feet from the Virgin River Valley, and 9,000 acre-feet from Coyote Springs. The authority also is exploring ways to capture, treat and use storm water that collects in newly built Las Vegas detention basins during infrequent rains.

But none of these sources can be used today. Brothers said the pipelines that would move water from Coyote Springs, 50 miles north of Las Vegas, to the valley haven't been built, and would take at least five years to complete.

Steve Glazer, chairman of the Sierra Club Colorado River Task Force, doesn't believe such planning will save Nevada in the long run. Glazer contends the authority's planning approach is lopsided, doing little to address unfettered growth, the biggest strain on the precious resource. "Las Vegas water providers need to focus more on demand management and not just rely on supply management," Glazer said. "That means using what little supply we have more prudently. It requires more conservation, and we've got to start recognizing our limits."