So money does make a kind of sustainability possible for Las Vegas. On the other hand, buying water is quite unlike buying anything else. At the moment, water doesn’t really function like a private good; its value, which Peter Binney calls “infinite,” is often only vaguely related to its price, which can vary from 50 cents an acre-foot (what Mulroy pays to take water from Lake Mead) to $12,000 an acre-foot (the most Binney has paid farmers in Colorado for their rights). Moreover, water is so necessary to human life, and hence so heavily subsidized and regulated, that it can’t really be bought and sold freely across state lines. (Enron tried to start a water market called Azurix in the late 1990s, only to see it fail spectacularly.) The more successful water markets have instead been local, like one in the late 1980s in California, where farmers agreed to reduce their water use and sell the savings to a state water bank. Mulroy and Binney each told me they think a true free-market water exchange would create too many winners and losers. “What you would have is affluent communities being able to buy the lifeblood right out from under those that are less well heeled,” Mulroy said. More practical, in her mind, would be a regional market that gives states, cities and farmers greater freedom to strike mutually beneficial agreements, but with protections so that municipalities aren’t pitted against one another.

More-efficient water markets might ease shortages, but they can’t replace a big city’s principal source. What if, I asked Mulroy, Lake Mead drained nearly to the bottom? Even if drought conditions ease over the next year or two, several people I spoke with think the odds are greater that Lake Powell, the 27-million-acre-foot reservoir that supplies Lake Mead, will drop to unusable levels before it ever fills again. Mulroy didn’t immediately dismiss the possibility; she is certain that the reduced circumstances of the two big Western reservoirs are tied to global warming and that Las Vegas is this country’s first victim of climate change. An empty Lake Mead, she began, would mean there is nothing in Lake Powell.

“It’s well outside probabilities,” she said — but it could happen. “In that case, it’s not just a Las Vegas problem. You have three entire states wiped out: Arizona, California and Nevada. Because you can’t replace those volumes with desalted ocean water.” What seems more likely, she said, is that the legal framework governing the Colorado River would preclude such a dire turn of events. Recently, the states that use the Colorado reached a tentative agreement that guarantees Lake Mead will remain partly full under current conditions, even if upstream users have to cut back their withdrawals as a result. The deal supplements a more fundamental understanding that dates to the 1920s. If the river is failing to carry a certain, guaranteed volume of water to Lee’s Ferry, which is just below Lake Powell, the river’s lower-basin states (Nevada, Arizona and California) can legally force the upper-basin states (Colorado, Wyoming, New Mexico and Utah) to reduce or stop their water withdrawals. This contingency, known as a “compact call,” sets the lower-basin states against the upper, but it has never occurred; it is deeply feared by many water managers, because it would ravage the fragile relationship among states and almost certainly lead to a scrum of lawsuits. Yet, last year water managers in Colorado began meeting for the first time to discuss the possibility. In our conversations, Mulroy denied that there would be a compact call, but she pointed out that Las Vegas’s groundwater and desalination plans were going ahead anyway for precautionary reasons.

I asked if limiting the growth of the Las Vegas metro area wouldn’t help. Mulroy bristled. “This country is going to have 100 million additional people in it in the next 25 to 30 years,” she replied. “Tell me where they’re supposed to go. Seriously. Every community says, ‘Not here,’ ‘No growth here,’ ‘There’s too many people here already.’ For a large urban area that is the core economic hub of any particular area, to even attempt to throw up walls? I’m not sure it can be done.” Besides, she added, the problem isn’t growth alone: “We have an exploding human population, and we have a shrinking clean-water supply. Those are on colliding paths. This is not just a Las Vegas issue. This is a microcosm of a much larger issue.” Americans, she went on to say, are the most voracious users of natural resources in the world. Maybe we need to talk about that as well. “The people who move to the West today need to realize they’re moving into a desert,” Mulroy said. “If they want to live in a desert, they have to adapt to a desert lifestyle.” That means a shift from the mindset of the 1930s, when the federal government encouraged people to settle in the West, plant water-intensive crops and make it look like the East Coast. It means landscapes of parched dirt. It means mesquite bushes and palo verde trees for vegetation. It means recycled water. It means gravel lawns. It is the West’s new deal, she seemed to be saying, and I got the feeling that for Mulroy it means that every blade of grass in her state would soon be gone.

The first impulse when confronted with the West’s water problems may be to wonder how, as scarcity becomes more acute, the region will engineer its way back to health. What can be built, what can technology accomplish, to ease any shortages? Yet this is almost certainly the wrong way to think about the situation. To be sure, construction projects like a pipeline from east-central Nevada could help Las Vegas. But the larger difficulty facing Pat Mulroy and Peter Binney, as they describe it, is re-engineering the culture and conventions of the West before it becomes too late. Whether or not there is enough water in the region for, say, the next 30 or 50 years isn’t necessarily a question with a yes-or-no answer. The water managers I spoke with believe the total volume of available water could be great enough to sustain the cities, many farms and perhaps the natural flow of the area’s rivers. But it’s not unreasonable to assume that if things continue as they have — with so much water going to agriculture; with conservation only beginning to take hold among residents, industry and farmers; with supplies diminishing slowly but steadily as the Earth warms; with the population growing faster than anywhere else in the United States; and with some of our most economically vital states constricted by antique water agreements — the region will become a topography of crisis and perhaps catastrophe. This is an old prophecy, dating back more than a century to one of the original American explorers of the West, John Wesley Powell, who doubted the territory could support large populations and intense development. (Powell presciently argued that river basins, not arbitrary mapmakers, should determine the boundaries of the Western states, in order to avoid inevitable conflicts over water.) An earlier explorer, J. C. Ives, visited the present location of Hoover Dam, between Arizona and Nevada, in 1857. The desiccated landscape was “valueless,” Ives reported. “There is nothing there to do but leave.”

Roger Pulwarty, for his part, rejects the notion of environmental determinism. Nature, in other words, isn’t inexorably pushing the region into a grim, suffering century. Things can be done. Redoubling efforts to prevent further climate change, Pulwarty says, is one place to start; another is getting the states that share the Colorado River to reach cooperative arrangements, as they have begun to discuss, for coping with long-term droughts. Other parts of the solution are less obvious. To Peter Gleick, head of the Pacific Institute, a nonprofit based in Oakland, Calif., that focuses on global water issues, whether we can adapt to a drier future depends on whether we can rethink the functions, and value, of fresh water. Can we can do the same things using less of it? How we use our water, Gleick believes, is considerably more complex than it appears. First of all, there are consumptive and nonconsumptive uses of water. Consumptive use, roughly speaking, refers to water taken from a reservoir that cannot be recovered. “It’s embedded in a product like a liter of Coca-Cola, or it’s contaminated so badly we can’t reuse it,” Gleick says. In agriculture, the vast majority of water use is also consumptive, because it evaporates or transpires from crops into the atmosphere. Evaporated water may fall as rain 1,000 miles away — that’s how Earth’s water cycle works — but it is gone locally. A similar consumptive process characterizes the water we put on our lawns or gardens: it mostly disappears. Meanwhile, most of the water used by metropolitan areas is nonconsumptive. It goes down the drain and empties into nearby rivers, like Colorado’s South Platte, as treated wastewater.

Gleick calls the Colorado River “the most complicated water system in the world,” and he isn’t convinced it will be easy, or practical, to change the laws that govern its usage. “But I think it’s less hard to change how we use water,” he says. He accepts that climate change is confronting the West with serious problems. (He was also one of the country’s first scientists, in the mid-1980s, to point out that reductions in mountain snowpack could present huge challenges.) He makes a persuasive case, however, that there are immense opportunities — even in cities like Las Vegas, which has made strides in conservation — to reduce both consumptive and nonconsumptive demand for water. These include installing more low-flow home appliances and adopting more efficient irrigation methods. And they include economic tools too: for example, many municipalities have reduced consumption by making water more expensive (the more you use, the higher your per-gallon rate). The United States uses less water than it did 25 years ago, Gleick points out: “We haven’t even paid too much attention to it, and we’ve accomplished this.” To go further, he says he believes we could alter not only demand but also supply. “Treated wastewater isn’t a liability, it’s an asset,” he says. We don’t need potable water to flush our toilets or water our lawns. “One might say that’s a ridiculous use of potable water. In fact, I might say that. But that’s the way we’ve set it up. And that’s going to change, that’s got to change, in this century.”