We use a LOT of water. Americans use more water per person than almost anywhere else in the world — more than three times as much as Chinese and 15 times more than the Danish. The highest domestic water use is in the driest Western states; Arizona residents use 147 gallons per day compared to just 51 gallons in Wisconsin.

And over-consumption is one big reason for the drought. Scientists project that the Southwest’s drought trends – which began in 2001 – could last for decades more and be the most severe in 1,000 years as climate change affects weather and water cycles.

But it’s not the only one. The West vastly overestimates the amount of water available to begin with. States in the Southwest get between a third to half of their water from groundwater. The rest comes from rivers and streams. But while ground and surface waters are often hydrologically interconnected, in many of those states, officials account for them as separate systems — meaning the best estimates of the region’s total supply could be wrong. Until last year, California didn’t even have a comprehensive law regulating how much water its residents took from aquifers underground, even though those waters now account for roughly half of the state’s total use.

As in, the West over-allocates Colorado River supplies by half a trillion gallons every year. The seven Colorado River states (Arizona, California, Colorado, New Mexico, Nevada, Utah and Wyoming) and Mexico divide up rights for 5.4 trillion gallons of river water each year — 1.4 trillion more than has actually flowed through the river each year on average since 2001 and 500 billion gallons a year more than the river produced, on average, long before the drought.

And demand is only expanding. Denver’s metro population hit 2.7 million in 2013, more than three times what it was in 1960, and it’s expected to grow by another 56 percent in the next 25 years. Several tunnels have already been drilled to divert Colorado River water beneath the Continental Divide to Denver, and Colorado lawmakers recently proposed constructing a new pipeline from the Missouri River. Explore the infrastructure supplying Denver’s water »

To make matters worse, the ways we withdraw water from the Colorado are inefficient. Utah’s Lake Powell, the second largest water storage facility in the U.S., holds up to 7.9 trillion gallons of water — but loses up to 292 billion gallons to seepage and evaporation every year. That’s 6 percent of the Colorado River’s entire flow. Meanwhile, moving Colorado River water to central Arizona requires more power than anything else in Arizona, contributing to the very climate warming that is diminishing the river’s supply. Explore the River »

They cause the very pollution that contributes to climate change and worsens drought. The Navajo Generating Station emits more carbon pollution than all but two other power plants in the United States, and was built largely to move Colorado River water to central Arizona. The station requires more power than anything else in the state, contributing to the very climate warming that is diminishing the river’s supply. Explore the River »

Technology has allowed us to pump ever more water from the ground. The invention of powerful motorized pumps made it possible to suck more groundwater, faster and from deeper than ever before. California’s groundwater levels have dropped 50 to 100 feet below the lowest levels ever previously recorded. In Arizona, groundwater levels have dropped as much as 500 feet, and the ground above them is sinking as the aquifers are emptied.

Urban development continues unabated. In 30 years, Las Vegas’ water district hasn’t rejected a single development proposal because of water supplies, allowing thousands of homes to be built as the population has nearly tripled. Vegas now supports its $103 billion economy with an average 138 billion gallons of imported water every year, almost entirely from Lake Mead. Explore Lake Mead »

Farmers profit from crops that can’t be sustained by the river’s natural flow. Farming and agriculture account for more than 70 percent of all water use by the Colorado River basin states. With its limited water, California farmers grow rice, cotton, alfalfa and almonds – four of the most water-intensive crops in the world. Read More: How Arizona Cotton Is Fueling the West's Water Crisis »

In fact, the federal government actually encourages farmers to grow water-hogging crops with Colorado River water. Since 1995, Congress has authorized more than $1 billion in federal subsidies to grow cotton in Arizona, and $3 billion to grow it in California. Cotton farmers say they might have switched, but the subsidies, from the Farm Bill, kept them in business. Read More: How Arizona Cotton Is Fueling the West's Water Crisis »

And states discourage conservation of the river with arcane “use it or lose it” clauses in their water laws. The Prior Appropriation Doctrine, the foundation of water law in the West, gave water to the first people to settle there. But state water laws based on this doctrine typically include an abandonment clause for their water rights, forcing farmers — whether they need their water or not — to “use it or lose it.”

Farmers could be more efficient, or stop planting crops that hog Colorado waters. Experts estimate Arizona could save more than 67 billion gallons of water each year by switching its cotton fields to wheat. It is also possible to grow Alfalfa, now one of the largest water users in the West, by simply applying less water, a change that would, save enough water to support 8.7 million people each year.

We could all eat less meat. A meat-based diet requires 30 percent more water than a vegetarian diet, and 90 percent of Americans eat meat. Research suggests meatless Mondays — or every American eating meat one less day a week — could reduce crop demand for feed and save an amount of water equal to the entire annual flow of the Colorado River each year.

Lawmakers could rethink the West’s flawed “use it or lose it” policy... Experts say only a tiny fraction of the 40 million people living in the Colorado River Basin control historic rights to take the river’s water. California’s Imperial Valley farming region, for instance, has 179,000 residents but gets a trillion gallons of Colorado River water each year while all of Nevada’s 2.8 million residents get only a tenth of that. Redistributing water rights — as Australia has done — enables them to address modern priorities.

...or create a competitive water market. If laws made it easier for farmers to trade their rights to water instead of wasting it or planting inefficient crops, experts say large supplies could be shifted to help meet cities’ needs. Related: Western Governors Weigh Water Transfers »

Federal, state and local governments could invest in new conservation technologies. The USDA has spent more than $200 billion since 1935 on conservation programs including sprinkler irrigation and other tools that can help ranchers dramatically reduce the amount of water they need to grow alfalfa. Expanding such programs would allow the West’s water to meet more needs.