(CNN) The people of El Paso, Texas, are resilient. Living in the middle of the harsh Chihuahuan Desert, the city has no other choice. On average, 15 days every year spike over 100 degrees Fahrenheit. The city gets little relief with annual rainfall of just about 9 inches. It's one of the hottest cities in the country.

One of its prime sources of water is the Rio Grande. Typically the river can supply as much as half of the city's water needs. But climate change is making that increasingly difficult and is pushing the city to look for new sources of water. Now, El Paso is on track to become the first large city in the United States to treat its sewage water and send it directly back into its taps.

Increasing temperatures will make the dry region even more vulnerable to drought, according to the federal government's most recent national climate assessment . Already challenged with balancing the demands of about 700,000 thirsty El Pasoans along with agriculture and industry needs, El Paso must also face the fact that climate change is literally drying up one of its major sources of water.

Analyzing tree ring records, scientists have been able to reconstruct the climate history of the region as far as the late 1500s and have found that as temperatures have risen, the amount of snow melting and feeding the Rio Grande has dropped.

"We're getting less runoff now than we would have gotten as recently as the '80s or '90s," said J. Phillip King, a professor of civil engineering at New Mexico State University. King has tracked the river's water levels for the past 27 years as an adviser to the Elephant Butte Irrigation District. The district manages the water distribution of some 90,000 acres of farmland along the Rio Grande Valley in New Mexico and Texas.

King told CNN Chief Medical Correspondent Dr. Sanjay Gupta that there is simply less snowmelt coming from northern New Mexico and southern Colorado to feed the river. Since 1958, the amount of early April snowmelt going into the Rio Grande has dropped 25% due to less snowpack and evaporation.

What's happening in the Rio Grande is not unique. It's a phenomenon happening throughout the Western United States.

King called the Rio Grande a harbinger of what's to come. "You know we've already gotten critically low here, and you can think of the Colorado as a few years away from a similar fate," he said.

Drought isn't anything new for the 1,800-mile long river. The Rio Grande has survived severe and sustained droughts, King said. But an increase in temperature is pushing both a warmer and dryer climate. And that means not only potentially less snowfall but a greater chance for water to evaporate.

The federal government projects that temperatures could rise an additional 8 degrees Fahrenheit in the region by 2100.

north of El Paso up to Colorado. It has a capacity of about 2 million acre feet, King said. The dwindling reserves are apparent at Elephant Butte Reservoir, just outside of Truth or Consequences, New Mexico. The reservoir there sits right on the Rio Grande and forms the largest recreational lake in the state. It holds water for farmers fromnorth of El Paso up to Colorado. It has a capacity of about 2 million acre feet, King said. Currently , it's hovering around 3% to 4% of its full capacity. Buildings that were built as offices during the dam's construction in the early part of the 20th century were previously submerged in the 1980s. Now, they serve as lookout points to a nearly empty basin.

Finding alternatives

For those who rely on the river, like the city of El Paso, they must look for alternative water sources out of necessity.

It is something that El Paso is used to. When Ed Acrhuleta took the helm of the El Paso Water utility in 1989, he knew that drought was an issue. To make a long-term plan, he needed a long-term outlook. An assessment by the Texas Water Development Board determined that the city could expect to run out of water by 2020 if it continued to rely on pumping groundwater out of its aquifers.

"I thought, we've got to reverse this mining of the aquifer. We've got to stabilize that aquifer. And we have to diversify our resources," he told Gupta.

Expanding the water portfolio was Archuleta's mission. Instead of relying solely on pumped groundwater, Archuleta expanded El Paso's water portfolio.

Farmers in the Western United States typically organized a system of rights or allotments to use water off of the river, including the Rio Grande. The rights were attached to property, so the El Paso utility began leasing water rights from farmers. The utility also bought farmland that carried those rights.

David Gutzler, a climatology professor at the University of New Mexico, likened an expanded water portfolio to a financial one. "If you can mix and match, then you use one or the other," Gutzler said. And it's the flexibility that ultimately makes cities more resilient, he said.

But in a move that was more visionary than just looking for water, Archuleta made water.

He lobbied the federal government for funds to create the world's largest inland desalination plant. The Kay Bailey Hutchison Desalination Plant is named after the Texas senator who helped Archuleta lobby in DC for the plant.

According to El Paso Water's hydrologists, under the 10 million acre feet of fresh water in the Hueco Bolson aquifer it relies on, there is an additional 30 million acre feet of brackish water that can be treated and used as drinking water.

It's estimated that the entire state of Texas has nearly 3 billion acre feet of salty groundwater to use. That's more than 20,000 times the amount of water El Paso used this year.

Producing water

Today, the Kay Bailey Hutchison Plant can produce up to 27 million gallons of water daily. The plant scales its production up and down based on how much water is available in the river and its aquifers. Next year, El Paso expects desalination to provide 7% to 9% of its water.

"This plant was built for growth. It was built for drought protection. It basically gives El Paso an insurance policy against drought," Archuleta said.

He also preached a gospel of conservation. He established community outreach programs with a mascot called Willie the Water Drop and created a museum about water for area children to visit and learn where their water came from.

The city paid residents to turn their grassy yards into rockscapes. The El Paso paper published the names of high water users.

When Archuleta retired in 2013, water consumption had dropped by about 35% per person. El Paso uses less total water now than it did 24 years ago, despite having 170,000 more people to serve.

Drinking treated sewage

Today, El Paso is ready to take the next step in expanding its water portfolio. It is building a closed loop system that will treat sewage water and turn it directly into drinking water. Among water professionals, it's called "direct potable reuse" or "advanced purification."

"It's the logical next step for us to take," said Gilbert Trejo, the chief technical officer of El Paso Water.

El Paso; Orange County, California; Scottsdale, Arizona, and several other utilities across the country treat sewage water and then pump it back into the aquifer to ultimately drink. Trejo says it can take about five years for the water to filter through the ground before being pumped back out and treated to the standards of clean drinking water.

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This treated water is also frequently used for irrigation and industrial purposes.

El Paso is building a completely closed loop facility; instead of being pumped back into the aquifer, the treated sewage water will undergo additional filtration and then be sent back into drinking water pipelines.

"We see this water that's clear and it's of good quality," Trejo explained to Gupta. "The next thing for us to do is to take a high-quality water we produce at a state-of-the-art facility and then treat it a little bit more with multiple treatment processes so we can drink it."

According to the EPA , the amount of wastewater produced in large cities can represent 50% to 60% of the total water supplied, providing a massive resource for cities like El Paso that are scouring for water.

clean of any pathogens or microbes, treated sewage water is sent through multiple steps of filtration, including UV and carbon filtration. To make sure the water isclean of any pathogens or microbes, treated sewage water is sent through multiple steps of filtration, including UV and carbon filtration. Studies have found that treated water is, in fact, less likely to have contaminants than untreated river or lake water.

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Efforts by other municipalities in Texas and California to use "direct potable reuse" haven't always gotten off the ground because of the "ickiness" factor. Community buy-in is key to getting these projects launched, said Justin Mattingly of the Water Research Foundation. "These are public agencies. They belong to the public. So you might as well ingratiate the public as well."

Archuelta's legacy of water conservation and education has primed El Paso for this moment.

"Everybody sees that we're in the desert that we're in an arid climate. Rain is scarce ... so when we tell our customers that we're doing everything possible and using every water resource around us to treat and make it safe for consumption, they take it pretty well."

By 2030, El Paso Water expects that desalination will produce 10% of its water supply, and 6% will of come from advanced purification.

Trejo told Gupta that it's not just the future for El Paso, it's the future for many other cities also faced with having to look for water.

"Technology allows us to treat [water] to a very high standard and makes it very safe to drink. Water really is all around us in every city."