If there is a Garden of Eden here, the place that gave Las Vegas life and from which it was ultimately exiled, it lies west of downtown, where wide, strip-mall-lined thoroughfares hem in neighborhoods of classic, low-slung ranch homes and palm-shaded mini mansions, mostly built in the '60s and '70s. Across a busy road from what is now a mega-shopping mall, cool, fresh water once bubbled up from a spring that an 1888 traveler described as "five yards in diameter and of unfathomable depth … below whose sparkling surface it was impossible to sink on account of the strong current that boiled up from the bottom."

In this unforgiving landscape, which gets half the rain Phoenix does, that spring made old Las Vegas an oasis, drawing the railroad and giving life to orchards and then a small city. Two dozen productive wells were sunk nearby, along with hundreds of smaller ones around the Las Vegas Valley. The population bloomed, and by 1962, had sucked the spring dry. Yet Las Vegans refused to give up their oasis. And for a while, they didn't have to.

The 1922 Compact that divided the waters of the Colorado River gave Nevada 300,000 acre-feet per year, far less than other states but seemingly enough for a sparsely populated state mostly occupied by federal land and bombing ranges. When the second intake in Lake Mead, the largest reservoir in the nation, was completed in 1983, Las Vegas Valley urbanites were able to take advantage of the state's entire Colorado River allotment.

Meanwhile, the advent of air conditioning caused the Southwest to boom. The population of Clark County, Vegas' home, was 273,000 in 1970. By 1990, it was nearly 800,000. Just as electricity imported from coal plants across the Southwest provided refuge from the broiling heat, Colorado River water kept the place verdant with golf courses, fountains and fake waterfalls. By the late '80s, each Las Vegan used more water than just about anyone else – almost 400 gallons per day compared to Phoenix's gluttonous 315 gallons. "The obsession in Vegas isn't money or sin," writes Charles Fishman in his 2011 The Big Thirst. It's water: "displaying it, unfurling it, playing with it, flaunting it." Or, as journalist Jacques Leslie observed after seeing the Bellagio fountain: Water in Vegas "is displayed more lasciviously than sex."

By the time charismatic, no-holds-barred water czar Pat Mulroy took over the then-newly formed Southern Nevada Water Authority in 1991, it was clear something had to give. Unlike Phoenix, Las Vegas no longer had nearby farms from which it could buy water. Either the 1922 Compact needed to be renegotiated – unlikely, given California and Arizona's growth – or Vegas would have to limit its own growth, unthinkable given homebuilding's pre-bust importance to the regional economy.

So Mulroy set out to prove that water does indeed flow uphill towards money, grabbing rights to 800,000 acre-feet from across the state, including groundwater under expansive valleys more than 200 miles to the north. But environmentalists, Indian tribes, ranchers and the two Utah counties that lie atop the aquifer have all bitterly fought "Pat's Pipeline." In December, a judge ordered the state engineer to reconsider his approval for the groundwater pumping. And with the southern Nevada economy still gasping from the recession, Las Vegas has a lot less gravity-defying cash available to build a project that could cost as much as $15 billion. The city's current share of water isn't guaranteed, either: Mead's level could drop below one of its two existing intakes by 2015 thanks to drought and growing demand. The Water Authority is spending $817 million building a new intake on the bottom of the reservoir, but if the climate continues to warm and dry, even that may prove inadequate.

Unlike many water buffaloes, however, Mulroy has, in many respects, also embraced camel-style conservation. With a bit of prodding, her constituents have followed. Per capita water use has dropped to 219 gallons – 40 percent less than in 1989. Between 2002 and 2012, the Las Vegas Valley grew by more than 400,000 people and added 25,000 hotel rooms. Annual visitation rose by 5 million, and yet total annual water use dropped 29 billion gallons.

Today, the Springs Preserve, a park, museum and educational center, sits about where the old fount bubbled up, and serves as a monument to the spring, a condemnation of the profligate water use of the past and a harbinger of a more efficient future. Next to solar panel-shaded parking lots and botanical gardens filled with native plants – panamint liveforever, scarlet hedgehog, desert spinystar – sits the Desert Living Center, a large, beautifully designed rammed-earth building with a catchment system to utilize what little rain falls from the all too sunny skies, and wetlands that filter water for re-use. Inside, kids can watch a dramatic flash flood simulation, crawl through a compost pile and play a video game whose goal is to tear up as much grass as possible, an activity, it turns out, that is key to Vegas' water-saving success.