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SEVEN states in the Southwest US are legally allowed to take water from the Colorado river: Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. But with the once-mighty river now running at historic lows, the states were given a to voluntarily agree to dramatic cuts in their use. On 31 January, they . Meanwhile, the low river flow has already slashed the power output of the iconic Hoover dam – once able to produce 2080 megawatts of hydropower, its generation has been .

Overuse and climate change have reduced the Colorado river to a trickle, while a decades-long in the desert Southwest has only increased demand for its water. The region’s rapid growth has never been sustainable, but in cities like Las Vegas and Phoenix have succeeded in curbing some of the water waste that could make the current crisis even worse. And since Arizona’s new water-conscious governor Katie Hobbs took office in January, she has revealed that the previous administration the state’s requirement that new housing developments guarantee water provision for 100 years.

But Hobbs and water experts across the Colorado river basin know that unchecked development is only the tip of the iceberg – and that agriculture is the real accounting for the vast majority of use of the Colorado river basin’s water. Water laws in the west of the US are as complex as they are arcane. But, for more than a century, they have facilitated the rise of unsustainable commercial agriculture across the region.

Ever since Arizona was first colonised, hubristic political leaders and entrepreneurs have profited from selling the idea that human ingenuity can engineer a solution to water shortfalls. This view is currently being sold to Arizona by an Israeli company, IDE Technologies, that promises to build a in Puerto Peñasco, Mexico – with water exported to Arizona via a 320-kilometre pipeline. This is ironic because the University of Arizona first started researching water desalination technologies in Puerto Peñasco .

What the Arizona team found was that large-scale desalination operations demand extraordinary amounts of energy. In the 1960s, the energy cost of desalinating seawater was unrealistic for the US. As I show in my book, , Arizona researchers started promoting joint desalination-greenhouse projects in the Arabian peninsula. There, diesel generators, then crude oil and later natural gas, could be used to power desalination plants.

Today, every city in the Arabian peninsula depends on vast desalination operations. But even there, where governments have practically free oil and gas, the is far too high for them to support large-scale agriculture. And where commercial farming has developed, this has lasted only so long as the groundwater reserves. In Saudi Arabia, that time has passed and the kingdom now sits atop .

This is precisely why the desert Southwest can’t just engineer itself out of its water crisis. If desalination can’t support commercial agriculture where the plants run on state-owned fossil fuels, it certainly can’t be supported in a region without cheap energy access. Meanwhile, have acquired land in Arizona to take advantage of the state’s lax water laws. Though this caused an uproar last year, the opposition of Arizona’s farmers to any groundwater regulation all but guarantees the state’s aquifers will run dry too.

Making the desert bloom through commercial farming has always been a romantic idea. But it has also always been a mirage.

Natalie Koch is a professor at Syracuse University and author of Arid Empire: The entangled fates of Arizona and Arabia