One afternoon last summer, Pat Mulroy stood in 106-degree heat at the broad concrete banister atop the Hoover Dam, the wall that holds back the mighty Colorado River, and with it the nation's largest reserve of water.

The reservoir is the brain stem of the system that helps sustain just about every person from here to San Diego. But as Mulroy looked out over the drought-beleaguered pool, then at 39 percent capacity, it appeared almost empty.

"Scary," Mulroy said.

Few people have played a greater role in determining how the reservoir's coveted and contested water supply has been used than Mulroy. Much of it has gone to nourish the Southwest's booming cities, and for 26 years, Mulroy was the chief arbiter of water for the fastest-growing city of them all, Las Vegas. As the head of the Las Vegas Valley Water District, she handled the day-to-day approval of water for new housing developments, emerald golf courses and towering casinos. As the general manager of the Southern Nevada Water Authority — a second job she held starting in 1993 — she also budgeted water for Las Vegas' future, helping to decide its limits. As the Water Authority's general director, Mulroy stretched her enormous influence over state bounds, shaping how Nevada negotiated with the six other states sharing Colorado River water.

Deploying a prickly wit and a rare willingness to speak truth about the water challenges hammering the Western states, Mulroy met head-on a reality few other leaders wished to face: that the Colorado River's ability to support the West's thirst to grow its economy and embrace the large population that came with it was not unbounded. She has been lionized for espousing conservation and pioneering a list of progressive urban water programs in Las Vegas while fiercely negotiating tough agreements between the states to use their water more efficiently and come to terms with having less.

But an examination of Mulroy's reign shows that, despite her conservation bona fides, she always had one paramount mission: to find more water for Las Vegas and use it to help the city keep expanding.

Mulroy wheeled and dealed, filing for rights to aquifers in northern Nevada for Las Vegas, and getting California to use less water while her city took more. She helped shape legislation that, over her time at the Water Authority, allowed Las Vegas' metropolitan footprint to more than double. She supported building expensive mechanisms with which to extract more water for the city's exploding needs – two tunnels out of Lake Mead and a proposed pipeline carrying groundwater from farms in the east of the state. Not once in her tenure did the Authority or the Las Vegas Valley Water District she ran beneath it reject a development proposal based on its use of water. The valley's total withdrawals from the Colorado River jumped by more than 60 percent on her watch.

Yet even last summer — staring at the effects of growth and drought on the reservoir, where once-drowned islands were visible for the first time in as much as 75 years — Mulroy apologized for none of it. She bridled at the idea that Las Vegas or other desert cities had reached the outer edge of what their environments could support.

"That's the silliest thing I have ever heard," she said, her voice rising in anger. "I've had it right up to here with all this 'Stop your growth.'"

ProPublica is exploring how the West's water crisis reflects man-made policies and management strategies as much, or possibly more, than it does drought and climate change.

Whether and how cities grow is one of the most decisive factors in determining the future of Western water supplies, and, to some extent, the nation's economy. For much of the last century the West has been guided by a sort of "bring 'em on" philosophy of the more people the better. Teddy Roosevelt first envisioned using the Colorado River's resources to move west a population the size of that day's Eastern Seaboard. They came in droves, supported by infrastructure the federal government built — including the Hoover Dam — and the water those facilities helped supply.

To an arid region blessed with little rain, the newcomers brought their Eastern tastes: Kentucky bluegrass planted across sprawling yards; fountains flowing with abundance; fruits and vegetables growing in an Eden-like oasis. Hundreds of thousands of settlers turned into tens of millions of people still dividing the same finite supply of water, one that was stretched thin from the very start. By the time it became apparent that growth might need to be controlled to be both productive and efficient, Western sprawl, like a sort of Frankenstein monster, had taken on a momentum of its own.

Los Angeles went through this spurt first, roaring through the 1920s with Hollywood's ascendance and having its own legendary water wars. Then came Phoenix and Denver. Las Vegas, in many ways, was last. But in its story the tensions are the strongest, the lessons the loudest and the crisis the most imminent.

It is all the more powerful because the person charged with managing Las Vegas' water strategy was Mulroy, whose knowledge and moxie suggested she better than almost anyone could tackle the quandary Western cities had gotten themselves into.

Mulroy, of course, was not the emperor of Las Vegas. She did not have autonomy over every decision the city made about growth. But she did have enormous say.

Dina Titus, the U.S. congresswoman who represents Las Vegas, thinks Mulroy squandered her chance to get ahead of the water problem by managing growth, instead of supporting it unconditionally.

"The Water Authority had the attitude that if people come, they'll get the water, beg, borrow or steal," Titus said. "And that's what they set out to do with very little long-term concern for what the impact was going to be."

Today Las Vegas is on the brink of a new building binge, and Mulroy, 62, remains uncompromisingly bullish. Standing 5-foot-5, her gray-blond hair wilting in the sweltering sunshine, her upper lip curled as she contemplated the idea that the city should rein itself in. Water can be found, she said emphatically, standing over the near-empty reservoir. Without growth, cities have no jobs and no future to offer coming generations.

"You have Detroit," she warned. "There isn't a city in the country or the world that wants to be Detroit."

Pat Mulroy first landed in Las Vegas in 1974, getting a $50 room at the Desert Rose Motel and sleeping on a round bed with a red velvet comforter beneath a mirror mounted on the ceiling.

She had flown in from Frankfurt, Germany, where she was born and raised, to accept a scholarship to study German literature at the University of Nevada, Las Vegas. A narrow slit of windows was cut into the hotel's cinderblock wall and it looked away from Las Vegas Boulevard, into the desert. The morning after her arrival, Mulroy, 21 years old, spread the curtains, gazed outside and saw what looked like a lava pit. "Oh my god I'm on Mars," she recalled thinking.

Mulroy went on to earn first a bachelor's and then a master's degree at U.N.L.V. Initially, she said she intended to chase a career with the State Department, an interest she picked up from her father, who worked as a civilian in the Air Force. He was an Irish Catholic Kennedy Democrat. Her mother was German but had grown up in India, spoke five languages and worked as a housekeeper and sometimes-translator for Gen. Dwight D. Eisenhower. Together they had instilled a no-limits mentality in their daughter.

"The notion that because you were born a certain way mattered didn't exist in my house," she said.

But then a friend of her father's at the U.S. Embassy in Bonn told her that a woman would never rise in the diplomatic corps. She was momentarily disillusioned, and turned her focus to studying in the United States.

After later dropping out of her doctorate program at Stanford to help raise money to send her sister to college, she returned to Las Vegas and took a $13,000-a-year job as a junior management analyst with Clark County. She became part of the county's legislative team, lobbying for tax and governance bills up in Carson City.

It was impossible to work for Las Vegas-area government and not find yourself staring at the underbelly of Nevada's culture. Gangsters walked the halls of the county seat, crowding hearings or petitioning the commissioners for their building projects. "Where do you find people to build a gaming industry those days?" she asked. "It was with the mob."

"I knew Moe Dalitz, I knew Morris Shenker. I had to deal with Tony Spilotro," Mulroy went on, ticking off some of the most notorious criminals and mob associates in Nevada history. "Moe Dalitz was the greatest gentleman you ever wanted to meet. Tony Spilotro was a scumbag — a dirty, filthy scumbag."

Cash flowed like water in those days, she said, and early one morning before a county commission vote, her boss, in the hopes of keeping the process clean, dispatched her to retrieve envelopes off the desks of commissioners before they arrived to discover what was in them. The envelopes were each stuffed with 50 $100 bills.

In 1985, Mulroy was promoted out of a county administrative post to help run the Las Vegas Valley Water District, one of seven feuding water utilities that served Las Vegas and the rest of Clark County. When her boss lost the confidence of his board in 1989, she inherited the whole department. "I didn't want the job. I didn't have the self-confidence. I didn't think I could do it," she said recently. "It seemed daunting."

Indeed, Mulroy, though ambitious, had no engineering or environmental experience, and had thought little about water as a resource. She was 36 then, with two children younger than 3 years old at home. Her attention, as she put it, was "kind of split," and she was weighted by guilt for the hours she poured into work and just as torn about the hours she spent away from the office.

But the job was politics, not science, and that came to her naturally. She had learned that politics works through relationships, not rules, and she applied the lesson to her new position. The valley, back then, still had a quaintness to it, with a population of just 741,000 and a Las Vegas strip that looked little like it does today. There was no ersatz Eiffel Tower or Empire State Building and no Bellagio hotel, with its musically synchronized water cannons. As Las Vegas grew up and corporate bigwigs displaced mobsters as the city's ruling class, Mulroy prided herself on being a student of character.

"You develop an instinct and a political sixth sense. I can smell a phony a mile off," she says now. "The minute someone flatters you, back up, take a hard look. The more sweetness and niceties that come out of someone's mouth, especially if they don't know you, beware, don't get caught."

Shortly after Mulroy took charge of the Water District she learned that the people who ran her utility, as well as the valley's other water agencies, didn't know how much water the area had — let alone how much water they were committing to give out. The valley gets just four inches of rainfall a year. Moreover, the groundwater springs that once supplied Las Vegas had been drawn down so far the land was collapsing above them. Las Vegas depended on Lake Mead for almost all of its water, and Mulroy feared that with surging growth the city would soon need more than it was allowed to take.

Her fears were confirmed when consultants she hired as one of her first acts developed a set of models that produced a damning assessment of the area's water resources. Tapping all the water it had at the time, their models warned, Las Vegas would run out of water completely in five years. The Water District wasn't even sure it had enough water to deliver what it had promised to development projects already underway.

On Valentine's Day 1991, Mulroy took what seemed like a logical step: She placed a moratorium on new water commitments in Las Vegas, stomping on the brakes of the city's booming growth. For the first time, there would be no new construction permits issued for buildings, subdivisions or the city's signature open spaces: golf courses. Even the permitting for new casinos, the engine of the state's economy, would have to pause. Only projects that had already been approved would be allowed to proceed.

Within a day or two, she received an urgent phone call from casino magnate Steve Wynn beckoning her to his office in a suite at the Mirage hotel. Wynn, one of Nevada's most influential businessmen, told her Las Vegas couldn't attract investors to pay for new development if it couldn't assure them they'd be able to get the most basic of permits for their projects.

"He wanted to know what the hell was going on," Mulroy said.

To give Wynn the answer he wanted – that the moratorium was temporary – Mulroy needed to get more water. The federal Bureau of Reclamation, which controlled the water coming out of Lake Mead, might let the Las Vegas Valley take more, but not while the valley's utilities remained as disorganized as they were.

In a feat of diplomacy, Mulroy convinced the other six utilities that she could get each of them more water if they formed a single agency and let her negotiate for the group. The Southern Nevada Water Authority was born; Mulroy got more water, and a year after it began, she lifted the permitting freeze. She would never try to enact a moratorium on growth again.

Years later, she acknowledged that Wynn's challenge amounted to a charge to never slow down growth. And she is blunt about how she chose to respond to it.

"I would rather be strategic and not be Don Quixote swinging at windmills," Mulroy said of her dealings with the city's business leaders. "They want to be an economic engine. They want to be a major global city. That's their strategic plan. That's their vision of themselves. They want to be Los Angeles."

"Had we not done it, they would have found someone who would."

Once Mulroy realized there would be no stopping Las Vegas' growth, even temporarily, she attacked the challenge of meeting the city's growing need for water with equal measures of pragmatism and creativity.

Starting in 1989, she made a series of moves to increase the metro area's water supplies, immediately and into the future.

She quietly filed for virtually all of the unclaimed rural water rights across Nevada, water Las Vegas could eventually import. She swooped in a few years before an enormous Fort Mohave coal power plant closed and struck a deal to transfer the facility's long-term water rights to Las Vegas. And through the original deal brokered to get more water from the Bureau of Reclamation, she increased her agency's water budget by almost 70 percent by persuading the federal government to give Las Vegas credits for the waste water it poured back into Lake Mead.

The golf courses of Las Vegas are only the most vivid symbols of possibly reckless growth. (Christaan Felber, special to ProPublica)

When Nevada's governor appointed Mulroy to the state's negotiating team for the Colorado River, expanding her authority by giving her a role in discussions between the seven state governments sharing the Colorado, she directed her search for more water across state lines.

She negotiated innovative swaps in which water savings in one place could be conveyed to another. She used the Water Authority's resources to help pay to build a reservoir capturing excess river flow before it ran into Mexico from California, saving hundreds of millions of gallons of water, of which the Southern Nevada Water Authority got a significant share. She pushed Los Angeles and San Diego's utilities to learn to get by with less, which they did in part by paying California farmers to fallow some of their fields.

Over time, Mulroy became known for pressing her view that, when it came to the Colorado River, the interests and fates of all the basin states were inextricably intertwined, giving all a stake in conserving it.

"She became synonymous with water conservation and Nevada's quest to define itself with respect to water management," said John Wodraska, who headed Southern California's Metropolitan Water District during Mulroy's ascent.

Others, though, saw her deal-making largely as enabling Las Vegas to use an ever-expanding amount of water with little of the discipline and restraint she urged on others. Mulroy instituted what she calls "soft conservation" measures to save water in Las Vegas — advertising water savings on billboards, running community education programs and banning artificial lakes in new developments. But across the 1990s, the overall water consumed by the Las Vegas metro area grew by 61 percent.

"Everybody has a water supply, and we were living within ours," said Tina Shields, interim water department manager for the Imperial Irrigation District in California, one of the largest rights holders to Colorado River water and a frequent target of Mulroy's criticism. "Others needed to live within theirs."

Building in Las Vegas is heating up again, but the plan for how to supply adequate water for this latest expected boom depends on a controversial $3.2 billion pipeline that has not been built. (Christaan Felber, special to ProPublica)

Some of the resentment Mulroy engendered surely reflected her manner as much as her message. She could be bombastic and provocative. Her adversaries called her the Iron Maiden or the Water Witch. (Her staff gave her a broom and she mounted it on the wall in her office.) She wasn't afraid to antagonize those she saw as standing between Las Vegas and water she thought it was entitled to.

She angered Colorado officials by advertising in local newspapers to try to buy water from farmers there. She threatened to take California all the way to the U.S. Supreme Court if it kept diverting more water from the Colorado than it was supposed to. She blasted farmers in neighboring states for wasting water by flood-irrigating their hayfields.

"Pat Mulroy had what we called a command presence," said Richard Bryan, the former U.S. senator and former governor from Nevada. "She was knowledgeable, self-assured without being arrogant, and when she spoke, she spoke with authority."

By the end of the '90s, the Las Vegas that Mulroy helped enable was considerably bigger and more bustling than the one she first knew.

The Las Vegas Valley's population had nearly doubled during the decade, coming to exceed 1.3 million people. An average of 48,000 new homes were added each year to accommodate the influx, as were a dozen new casinos. Eight miles from downtown, the Howard Hughes Corporation began construction of Summerlin, a 22,500-acre suburban micro-community complete with schools, parks, shopping centers and nine golf courses.

Mulroy capped off the '90s by helping to shape the Southern Nevada Public Land Management Act, which cleared the way for still more growth.

Historically, Nevada's settlers claimed only two million acres of land within the state's borders, leaving the rest to federal control because it wasn't viable without water.

Legislation in 1998, advanced by Bryan and Nevada's other senator, Harry Reid, and then-congressman John Ensign, allowed the U.S. Department of the Interior to sell tens of thousands of acres of federal land to private developers, enabling Las Vegas Valley authorities to steer federal land sales they otherwise would not have the right to control. It thus also formally freed Las Vegas from old urban boundaries.

Mulroy was part of the brain trust that refined the bill, hosting several early meetings at the Water Authority to discuss it. She insisted that if Las Vegas' footprint was going to be larger, the Water Authority would need to add staff and infrastructure to supply water to the new areas. Her price: A 10 percent slice of the revenue from each lot sold. The Water Authority's haul from the sale of federal lands eventually came to almost $300 million and helped bolster financing for the pipelines, tunnels, pumps and more that Las Vegas eventually built to double its capacity to move water out of the Colorado River.

More controversially, it also allowed Mulroy to start buying up northern Nevada farmland, paying as much as $32 million for properties that previously sold for no more than a few hundred thousand dollars. With the land came the right to tap vast aquifers underneath it. The Southern Nevada Water Authority would eventually become one of the largest owners of ranch land in the state.

Mulroy says the 1998 federal legislation merely allowed Nevada a say in sales the government was pursuing anyway, but she does not deny that enormous growth followed. To enable it — or respond to it, as she says — Mulroy pushed big infrastructure investments that she describes as a turning point. "The second treatment plant, the second tunnel," she said, referring to the $2.1 billion project to expand the water intakes from Lake Mead, "that was the big growth spurt."

Las Vegas spilled into the space opened up by the 1998 land measure at an astonishing pace.

More than 34,000 acres were sold in the first decade after the act was passed, more than twice the size of Manhattan, and master-planned mini-cities appeared on the edges of the Las Vegas metro area. Neighborhoods teemed with bulldozers and paving machines and rang with a cacophony of nail guns and air compressors. Business leaders joked that the beeping backhoe had become Nevada's state bird.

To Rob Mrowka, who once worked as the Clark County Environmental Planning manager, it was all part of the "Western development-industrial complex."

"That whole vicious cycle just kept pushing the boundary out and out and then you need greater and greater services," said Mrowka, who is now a senior scientist with the Center for Biological Diversity, an environmental advocacy group that has sued to stop Mulroy's effort to import more water from upstate. "Elected officials didn't pay any attention to the long-term issues. It was always balls to the wall. The specter of rapid growth was like a mermaid sitting on a rock, calling."

In May 2002, Mulroy was in her large, corner office with views of the strip in the distance when her deputy, Kay Brothers, brought unexpected news.

"'We are walking right into a wrecking ball,'" Mulroy recalls Brothers saying. Abysmal snowpack in the Rockies would put about one-quarter the normal amount of water into the Colorado River that season.

The Water Authority relied on a 50-year water plan it updated every couple of years that was supposed to project the area's need for water against population growth and infrastructure demands. The plan was dependent on a stopgap measure Mulroy had negotiated: Nevada's ability to take a share of excess river water left unclaimed by the other states.

The Water Authority had allowed a tsunami of growth on the belief that their figures were unassailable. But the Authority's forecasts — which Mulroy says were based on data given to them by the Bureau of Reclamation — had failed to anticipate the risk that a severe drought could affect the Colorado basin. The surplus water they had anticipated had suddenly evaporated. The development plan Mulroy had placed confidence in for the next half-century was suddenly worthless.

"The drought changed everything," Mulroy said.

Mulroy moved beyond public awareness campaigns and began to crack down on profligate residential and recreational water use in Las Vegas more aggressively. She banned the lush green lawns that had typically lined the city's newly developed suburban streets and offered cash incentives for homeowners to rip out their existing lawns. She also barred fountains and ornamental waterfalls, the kind that decorated just about every hotel and a good number of upscale communities. She installed watering restrictions for golf courses and demanded that new housing developments meet water efficiency guidelines.

"Conservation had to stop being a luxury and something we journeyed into slowly, but something that had to be kick-started in a very different way," Mulroy said.

She became almost evangelical about climate change – something she had previously described as "not an exact science"– and implored her counterparts in the other river states to plan for the threat it posed to Southwestern cities. "We have no rearview mirrors anymore," she told ProPublica in a 2008 interview. "All the old probabilities, throw them away. We are walking into a dramatically shifting climate and that is fundamentally going to change everything."

Mulroy even rallied the gaming and development companies to conserve water. Wynn, forever an ally, made phone calls on her behalf, helping to raise funds to further her public relations campaign and fill billboards across Las Vegas with appeals to save water and heed the drought.

By some measures, Mulroy's conservation push was successful. Las Vegas residents served by the water district reduced their water use from 314 gallons per person per day in 2003 to around 205 gallons (a figure still 30 percent more than in Los Angeles, and more than three times what San Francisco metropolitan area residents use each day.) Mulroy argues that the water Las Vegas recycles should be factored in, a calculation that lowers use in the valley to merely twice that of San Francisco residents. Las Vegas' net water consumption, as long as you subtract that water recycled back into Lake Mead, began to decline.

But the drought didn't go away. Lake Mead's levels steadily dropped by nearly one foot every month. The seven river states began to talk about an emergency shortage declaration, in which water deliveries throughout the Southwest would be cut back.

Through it all, Las Vegas' building boom continued, fueled by increasing casino revenue, a spike in tourist visits and a seemingly irrational mortgage and real estate market.

The casinos employed huge numbers of service industry workers. The workers needed housing. By 2008 there were about 200,000 more homes in the valley than there were in 2000, and every new development served by the Las Vegas Valley Water District received a water commitment letter agreeing to hook up water. Other utilities serving parts of the valley under the Water Authority acted similarly.

Mulroy maintains that she had no real opportunity to thwart building, even if she had wanted to.

"We can't pick and choose who gets water and who doesn't," she said. "Whoever gets zoned, whoever gets the business licensing, whoever gets approval, we have to service. They come to us courtesy of county and city zoning."

She referred ProPublica to the Water District's service rules which lay out her legal authority, but those rules state that the "District may deny any request for a water commitment or request for a water connection if the District has an inadequate supply of water."

It was certainly true that the local officials in charge of planning and zoning had little or no interest in taking on the casino and building industries that benefited most from growth.

In 2003, one former Clark County commissioner, Erin Kenny, got caught accepting more than $25,000 from a strip club developer with business before the commission, then implicated her colleagues, testifying that such bribes were common. Kenny and two other commissioners went to prison.

"Growth was abundant, it was rabid, it was almost unstoppable," Kenny said in a recent interview.

To this day, candidates for Clark County and other area commission seats get a substantial amount of their political contributions from the building and development industry. The commissioners not only make the most important decisions about growth, they also sit on the boards of the water utilities, including the Water Authority, controlling decisions on water use in the Las Vegas Valley. Furthermore, some of the most significant new housing developments built in Las Vegas — accounting for thousands of new homes — were built in places where planning officials approved zoning changes to allow higher-density building.

"The money from the gaming industry and the money from developers, they controlled the politics," said Don Williams, a one-time campaign manager for Harry Reid and a veteran Las Vegas area political analyst. "The casinos wanted to control planning. They didn't elect people who were interested in slowing things down for the good of the area."

The industry's response to any measure seen as anti-growth could be virulent. Titus, the local congresswoman, says she was once pictured on the cover of a construction trade magazine with a noose around her neck after she pushed for growth restrictions and then passed a bill as a state senator that restricted re-zoning rural land for high-density construction.

Still, Titus was disappointed by the Water Authority's complicity in the headlong rush to build. "It was one and the same with the local government," Titus said. "They encouraged the growth and accommodated the growth and found ways to foster the growth. They thought of that as the goal."

Many were surprised and disillusioned by Mulroy's acquiescence, especially after her persistent efforts to advance conservation, both in Las Vegas and among the seven states that shared the Colorado River. Her department signed off on an endless procession of development proposals, based on the notion that as long as they met the standard water efficiency criteria she had helped the county set up, all projects were equal.

Neither the Water Authority nor the Clark County zoning department factors the total amount of water a new project will require into its permitting decision. They do not prioritize water-efficient developments over others, instead approving proposals on a first-come-first-served basis as long as they comply with zoning categories and more generic efficiency guidelines.

Chris Giunchigliani, a current Clark County commissioner who once served on the Water Authority board, sees the agency — which she called "the final arbiter" of what can and should be built — as centrally responsible for why Las Vegas' building boom continued through the drought years.

Still, she empathizes with Mulroy's predicament.

"When a city thinks the only way they can generate a tax base is by generating growth, the word is, 'Don't tell us we can't do this,'" she said. It's "'Find a way to make it possible.'"

Growth stalled briefly in the Las Vegas Valley during the 2008–2009 financial crisis, but is heating up again.

Though the Water Authority has managed to reduce its overall water consumption since the drought began in 2002, the Las Vegas Valley used 1.2 billion gallons more water in 2014 than in 2011. According to a recent report from the U.S. Conference of Mayors, the valley is expected to add another 1.3 million people by 2042. By the Water Authority's own demand projections, that growth will translate into taking at least 240 billion gallons of water each year, 74 percent more than Las Vegas demands today.

As a consequence, the ranch land bought up by the Water Authority in northern Nevada could be seen as Mulroy's parting gift to her parched city. But getting the water underneath that land to Las Vegas will require building a $3.2 billion pipeline across half the state, an idea that has generated immense controversy.

Some experts fear that if the city taps this water supply, it will suck dry wetlands that support valuable species, cripple farm communities and possibly cause ground across the Great Basin valley to subside. But the pipeline's supporters herald it as a visionary step towards reducing Las Vegas' near-universal dependence on the Colorado River. "We really need to diversify our resources," said Bronson Mack, the Water Authority's spokesman.

The debate provides a frame for assessing Mulroy's legacy.

Before she ran the Las Vegas Valley's water supply, the city's environmental constraints seemed insurmountable. But Mulroy demonstrated that with enough money, savvy and will, almost any limit could be overcome. In 1991, warned she had five years of water, she deployed creative accounting to maximize every possible gallon of water credit the city could muster. In the mid–2000's — faced with a renewed crisis — she again found water by taking it out of residents' lawns and fountains. In a sense, she pulled off a miracle. Las Vegas absorbed nearly three decades of astronomical growth with the water it had, and it did it in the midst of the worst drought in a generation.

"She is the prophet of growth," said Bruce Babbitt, the former governor of Arizona and former U.S. Secretary of the Interior, who has worked both with and against Mulroy on various projects. "No question."

But what will happen next? Lake Mead reached its lowest level since 1937 last month. Today the lake is just 20 inches above the level that can trigger a formal emergency declaration. If levels drop past that point on Jan. 1, 2016, something the government forecasts as a one-in-three chance, the federal government will declare a shortage and Nevada and Arizona will face dramatic cuts in supply.

When Mulroy stood above the Hoover Dam last summer, looking down at the shocking white 148-foot-tall bathtub rings lining the orange sandstone walls of the dwindling reservoir, it hardly looked as though the strategy that had worked for the past two decades would work in the future.

"Las Vegas and Southern Nevada have been a harbinger," said Wodraska, the former L.A. water chief, reflecting on the push to turn so much of the arid West into cities. "You're in a desert. I think we're going to look back and shake our heads and say, 'What were we thinking when we tried to create this artificial environment that just is not sustainable?'"

The Southern Nevada Water Authority's most recent 50-year water plan once again aims to outline how the area's water resources can meet the needs of its population and economy. In six charts presented in the document, there is no scenario the Water Authority could conceive in which demand for water does not significantly outstrip the current supply, unless it completes the pipeline and begins to harvest water from other parts of the state.

That reality seems to have provoked desperate measures. The Water Authority is finishing a $1.4 billion tunnel and pumping station that amounts to a drain hole in the bottom of Lake Mead, a project Mulroy describes as "a survival policy," that would allow the city to continue taking water even after the generators and pumps in the Hoover Dam stop operating and California, Arizona and Mexico, which is also entitled to the tail end of the Colorado's water, are completely cut off. "We'll still be pumping," Mulroy said. "You better be able to take the last drop."

In February 2014, Mulroy retired, saying she was tired of fighting Las Vegas' water battle, which she described as constantly in crisis. She nominated as her successor her senior deputy general manager, John Entsminger, a lawyer experienced with interstate Colorado River negotiations and known to be a supporter of Mulroy's water management strategy.

In her last days at the Water Authority, Mulroy began to talk about the drought as a natural disaster — like a flood, which often garners federal aid money and a swift emergency response — just slower moving. If the federal government made disaster money available for droughts, she thought, it could help in water conservation and water purchases. "This is as much an extreme weather event as Sandy was on the East Coast," she told The Las Vegas Review Journal in 2013.

These days, Mulroy is a senior fellow with the Brookings Institution, where she focuses on climate adaptation and global water policy. She is particularly interested in scaling up her experience in the Colorado basin, examining what a projected nine billion people inhabiting the planet will mean for its water supplies. But she is still involved in Colorado River issues daily.

In a sort of stump speech she has delivered to audiences around the world, she advocates what she calls a "mosaic" approach to the West's water problems. It involves a little bit of everything: a slice of conservation, some compromise by farmers, some new groundwater wells and so on.

Some of the mosaic tiles — like projects to desalinate ocean water, pipelines to move water west from the Mississippi River or seeding rain clouds with silver iodide — stretch technological limits and call for innovation. In some cases they demand positive, even wishful, thinking.

"Right now, we don't have the luxury to take any options off the table," she said.

The one concept she holds as an exception, however, is limiting growth. It won't be limited for Las Vegas. Or for the rest of the Colorado River basin. Not ever. To Mulroy, suggesting such a notion would be tantamount to accepting that human progress can be limited or dictated by nature.

Even with the evidence of the water crisis right in front of her, she's just not there yet.

"We live in a free country where people can move wherever they want," she said. "I can build a de-salter. I can cause more conservation. I can't slow growth and manage growth. I'm not going to waste a lot of time trying to create something that stands in exact contradiction to an ever-exploding human population."