The Palo Verde plant, Arizona’s only nuclear power facility, relies mostly on effluent. Only about 3 percent of the water used in its operations came from groundwater in 2013, according to Arizona Public Service.

TONOPAH — Many scientists and engineers consider the Palo Verde Nuclear Generating Station to be a feat of engineering because it’s not near a large body of water, unlike other nuclear power plants around the world.

The plant’s three nuclear reactors each require 20,000 gallons of water per minute.

But much of the Southwest faces a drought. So where does the water come from?

The vast majority comes from wastewater. The power plant’s wastewater comes from Phoenix’s 91st Avenue wastewater treatment facility and Tolleson’s facility. The water moves through about 36 miles of pipe before it reaches the plant in Tonopah, about 50 miles west of Phoenix.

The nuclear fission process creates incredible amounts of heat, so when the reaction takes place under water, a heavy mass of vapor rises, turning the turbines that generate electricity.

“If we bring a drop of water to Palo Verde, it either evaporates off or it stays here forever,” said Mike McLaughlin, general manager at the plant. “We’re a zero-discharge station, which is a little bit unusual since most stations are near the ocean or a river, and they’re pumping water into and out of the station.”

He said he likes to watch the vapor stream out like giant chimneys.

“(The) higher the humidity and lower the temperature, the bigger the plume coming from the cooling towers,” McLaughlin said.

The plant, in commercial operation since 1986, produces power for about 4.1 million people across regions in New Mexico, Texas, California and Arizona.

Each of the turbines within the reactors generates 1,400 megawatts of power, or about 1.7 million horsepower.

“That can get a little confusing. I mean, a high-performance sports car only generates just a few hundred horsepower,” McLaughlin said.

Seven Southwestern companies own the plant, but Arizona Public Service owns the largest share — with about 30 percent — so it takes the most responsibility for the oversight and upkeep of resources.

Although the plant relies mostly on effluent, about 3 percent of the water used in its operations came from groundwater in 2013, according to APS.

Robert Lotts, water resource manager for APS, said his company carefully monitors water levels throughout the state so it can reimburse municipalities for any water APS purchases.

“They have dams where they measure the depth,” Lotts said. “We have actual flow measuring technology, too, so we can see how fast water is moving.”

Lotts said the company is concerned about the state’s drought, but he thinks the current system saves potable water while making the most of treated wastewater.

At peak operating capacity, Lotts said the plant uses about 80 million gallons of water to generate power during a typical hot day in July or August. According to APS records, at 5 p.m. on Aug. 5, about 1.2 million APS customers used more electricity than at any other time in 2015.

Still, nuclear power has its critics.

Sandy Bahr, director of the Sierra Club’s Grand Canyon Chapter, said she would like to see less water used at the plant and more going to replenish rivers and reservoirs.

“I suppose you could say it’s good that they aren’t using groundwater,” Bahr said. “But you have to think about what other uses could be.”

Arizona still suffers from drought-like conditions throughout the state, and with Lake Mead and the Colorado River watershed at low levels, Bahr said there must be a more efficient way to use water.

“It takes a lot of water to generate electricity,” she said. “But it also costs a lot of electricity to move water. If we can reduce water consumption, we can reduce electricity use.”

Bahr said she would like to see consumers and businesses use more photovoltaic solar panels because they require much less water to function.

“You have to wash the dust off of them every once and a while,” she said. “But that’s about it.”

Only 1.3 percent of the APS energy portfolio came from renewable energy in 2014, while 27.2 percent came from nuclear. Coal leads all sources with 33.5 percent, according to the company.

“One of the things we have plenty of is sunshine,” Bahr said. “But we still have a very low renewable energy standard.”

APS estimates that the Palo Verde plant generates energy equal to a 191.6-square mile field lined with solar panels, an area about the size of Scottsdale.

Solar still has issues when operating at such a large capacity, said Keith Holbert, an Arizona State University associate professor in the School of Electrical, Computer and Energy Engineering.

“In terms of scale, nuclear is essentially your only choice,” Holbert said. “With solar, the heat source happens to be the sun, and there’s a lower thermal efficiency.”

Holbert said he’s optimistic about the state’s energy future based on his own findings, what students have told him and changing public sentiments.

“In 20 or 30 years, there will be a greater acceptance of climate change and a need to solve it,” Holbert said. “Students are still excited about nuclear because it’s not causing climate change.”