Fifty miles south of the US border, on the edge of a city on the Gulf of California, a few acres of dusty scrub could determine Arizona’s future.

As the state’s two main sources of water, groundwater and the Colorado River, dwindle due to drought, climate change and overuse, officials are considering a hydrological Hail Mary: building a plant in Mexico to siphon salt from seawater, then piping hundreds of miles of largely uphill to Phoenix.

The idea of ​​building a desalination plant in Mexico has been discussed in Arizona for years. But now a $5 billion project proposed by an Israeli company is being seriously considered, a sign of how concerns about water scarcity are roiling policymakers in Arizona and across the American West.

On June 1, the state announced that the Phoenix area, the nation’s fastest-growing region, does not have enough ground water to support all future housing that has already been approved. Cities and developers who want to build more projects beyond what has already been permitted would have to find new sources of water.

State officials are considering whether to allocate an initial $750 million in desalination project costs, although Gov. Katie Hobbs, a Democrat, has yet to approve it.

“Desal in Mexico is a highly likely outcome for Arizona,” said Chuck Podolak, the state official responsible for finding new water sources. Last year, lawmakers agreed to give his agency, the Arizona Water Infrastructure Financing Authority 1 billion dollars for this mission. He said any water project that gets built “will look crazy and ambitious — until it’s done. And that’s our history in Arizona.”

Desalination plants are already common in coastal states like California, Texas, and Florida, and in more than 100 other countries. Israel gets more than 60 percent of its drinking water from the Mediterranean Sea.

The Arizona project would be unusual because of the distance and the fact that the state is landlocked. The water would have to travel about 200 miles and climb more than 2,000 feet along the way to reach Phoenix.

“We live in a world with gravity,” said Meagan Mauter, an associate professor of civil and environmental engineering at Stanford University and an expert on desalination. “When you have to move water, you have a huge fixed cost.”

The plant would allow Arizona to continue growing — but at a high price.

It would flood the northern Gulf of California with waste brine, threatening one of Mexico’s most productive fisheries. It would create a freeway-sized corridor through the US National Monument and UNESCO site, established to protect the fragile desert ecosystem. And the water it provided would cost about ten times more than water from the Colorado River.

In a sense, Arizona was already here. The state owes its boom to water projects on a superhuman scale, culminating in 336 miles, $4 billion aqueduct which carries water from the Colorado River to Phoenix and Tucson. IDE Technologies, the Israeli company behind the new desalination design, has picked up on that legacy, calling its project “an infinite and limitless reverse Colorado.”

This message found an audience. According to IDE, even before the groundwater shortage was announced, representatives from Phoenix and a half-dozen surrounding cities met with the company to learn about the project.

Environmentalists say that instead of importing water from another country, the state should protect its limited supply by having fewer lawns, fewer swimming pools and perhaps fewer houses.

“What Arizona really needs is to put in place stronger water protections,” said Miché Lozano, who until recently was the Arizona program manager for the National Parks Conservancy. “Pipelines are just such a big, stupid idea.

A nightmare for Arizona’s future

The proposed source of Arizona’s salvation is Puerto Peñasco, a city of 60,000 an hour south of the border. From the ocean, the city is a strip of luxury villas and high-rise apartments, fronted by soft beaches opening into turquoise water. Tourists from Phoenix, who make up the majority of visitors, call it by its anglicized name Rocky Point; its unofficial nickname is Arizona Beach.

But behind the glamor is a city of unpaved roads and low cinder block buildings, covered in dust and sand blown in from the desert around it. A third of the population lives in poverty. Among its other problems: Puerto Peñasco cannot provide enough drinking water for its own residents.

The city is a nightmare for Arizona’s own future. Due to the lack of surface water, it relies on underground aquifers, the supply of which has dwindled with the growing population. When tourism swells in the summer, the water pressure in the pipes drops; residents have to rely on whatever they managed to store in cisterns.

The Israeli company said it would provide some drinking water to Puerto Peñasco as part of its proposal, though not in what quantity or at what price. The head of the local water supplier, Héctor Acosta Félix, said that some kind of desalination project is vital for the future of Puerto Peñasco.

But one part of the plan poses a challenge: what to do with the waste.

Desalination works by vacuuming up huge volumes of ocean water and then forcing it under high pressure through a series of membranes to filter out the salt. Every 100 gallons of seawater produces about 50 gallons of potable water and another 50 gallons of brine, which has a salt content roughly twice that of seawater.

IDE would release this brine into the sea. In the open ocean, waste brine can be dispersed quickly. But because Puerto Peñasco is near the tip of the Gulf of California, which is actually a long, shallow bay, the effects could be concentrated.

This could harm plankton, which form the base of the food chain, said Nélida Barajas Acosta, head of environmental group CEDO Intercultural. More than half of Mexico’s fishing comes from the Gulf of California.

“The impacts on fisheries will be dramatic,” Ms Acosta said. “The water goes to the US, but the environmental impacts stay in Mexico.”

IDE, one of the world’s largest desalination companies, declined to comment for this story. But in public meetings with Arizona officials in December, company representatives dismissed the concerns.

The company asked Arizona to sign a 100-year agreement to buy water from the desalination project. In return, IDE says it will find private financing to cover the estimated $5 billion in initial costs to build the desalination plant and pipeline. The company is working with Goldman Sachs to secure this financing. Goldman Sachs did not respond to a request for comment.

Erez Hoter-Ishay, IDE’s project manager, said the release of brine will not harm ocean life and suggested it could even be beneficial. “In other resale facilities, we see life flourishing next to them,” he told lawmakers.

It is unclear whether Mexican officials would support the plan. The governor of Sonora, Alfonso Durazo, he said he was against it. But the national government has jurisdiction over the water in Mexico, and President Andrés Manuel López Obrador was quoted in January as having open to the idea.

Mr. Duraz’s office did not respond to a request for comment. Mr. López Obrador’s office referred questions to the National Water Commission, which did not respond.

Cross-section of the biosphere reserve

Getting Mexican approval may not be the biggest hurdle.

Between Puerto Peñasco and Phoenix lies one of the most ecologically fragile places in Arizona: Organ Cactus National Monument, a riot of velvety mesquite, bear cholla and red-flowered ocotilla, teeming with roadrunners, rattlesnakes and giant-eared rabbits, spilling over 500 square miles of the southern edge of the state like a crowded psychedelic fever dream.

UNESCO has declared a monument along with a national park on the Mexican side of the border, and biosphere reserve — an honor bestowed almost nowhere else in the southwestern United States. The pipe would cut through the middle of it.

And not just pipes. Desalination plants require a huge amount of energy. To power the plant, IDE would build one of America’s largest solar farms near Phoenix, plus a transmission line to move that energy to Mexico. That line would need a 150-foot-wide right-of-way corridor, a project consultant told officials in December. The water line would require a 175-foot corridor.

The U.S. Bureau of Land Management is reviewing an application from IDE to build these lines through the park.

“We’re bypassing wilderness areas,” Mr. Hoter-Ishay told lawmakers. He did not explain what that meant or how it would be done.

In addition to its ecological value, the land has spiritual significance to the Tohono O’odham Nation, whose people lived there for thousands of years before being displaced to a reservation east of the park.

On a recent morning, Lorraine Eiler, a tribal representative, wandered through the area of ​​the park where her ancestors lived. Endangered terrapins and hatchlings roamed the spring-fed pond; the branches of gorse bushes bent with orange-red fruits the size of jelly. Saguaro cacti rose overhead, their stubby arms thrust up like startled giants.

Ms. Eiler said the O’odham believe each saguaro embodies the human spirit. The pipeline would require uprooting countless saguaros. “When you knock one down, it’s like knocking you down,” she said.

Among the saguaros, she was joined by Mr. Lozano, who was more outgoing.

“To have a private foreign company come in and run a binational pipeline through two UNESCO Biosphere Reserves with endangered species just doesn’t seem like a great idea,” Lozano said. “It’s just me.

‘Crazy and Ambitious’

Ninety miles north of Organ Pipe, land was being prepared for construction in Buckeye, an outer suburb of Phoenix. As of 2010, the city’s population has doubled to over 100,000; officials say it could eventually reach one million.

Those residents will need water — and Buckeye’s options are dwindling. The Arizona Water Department put it there in January did not have enough ground water under Buckeye to support new homes beyond the construction that has already been approved.

The IDE pipeline, which would run around town, is basically a bid to keep places like Buckeye viable. Terry Lowe, the city’s director of water resources, said the cost of that water is probably too high for now. But as Buckeye continues to grow, he expects that could change.

“The deal with Arizona water is not how much water there is,” Mr. Lowe said. “It’s about how much we want to pay for it.”

Arizona has a big Buckeye. Arizona’s population has jumped nearly 50 percent since the Great Drought began in 2000 and shows no signs of stopping.

IDE’s proposal is so far the only formal bid submitted to the state agency seeking to secure more water. While no decision has been made and Mr. Podolák says he wants other proposals, he said some version of the plan is likely eventually.

In the sprawling metropolis in front of his office, houses continued to rise.

Steve Fisher contributed reporting from Mexico City.