The Santa Cruz River was once the lifeblood of Tucson, Arizona. Due to heavy development and groundwater overdraft, it hasn’t seen year-round flow in 70 years. The city plans to revive the storied desert river with recycled effluent.

Recycled wastewater is gaining wider acceptance to boost drinking water supplies across the arid West. Now a project in Tucson could mark another milestone: The city wants to use recycled effluent largely for ornamental purposes.

Tucson proposes to use a portion of the metro area’s treated urban wastewater to make the Santa Cruz River flow through downtown again for the first time in 70 years. The river once meandered year-round through this Sonoran Desert town. But it has been reduced to a dusty flood-control channel by more than a century of groundwater pumping and development.

Known as the Santa Cruz River Heritage Project, the goal of the city project is to bring back some of the historical riparian habitat and aquatic character that once made Tucson a haven among desert cities.

“We’re using it as ornamental. We want it to attract people,” said Maya Teyechea, a hydrologist with Tucson Water, the city’s water utility. “We’re not necessarily trying to get people to buy into drinking it at this point.”

The project awaits a permit from the state of Arizona, which must approve such uses of recycled wastewater. After that, little is required to make the river flow again. Pipes carrying recycled wastewater – currently used for landscape irrigation – already flow near the river at strategic points. The city merely has to tap those pipes and build a small treatment facility near the river to extract chlorine from the wastewater, which could be harmful to aquatic life.

No difficulty is expected in obtaining the state permit, said Teyechea. And there has been no community resistance to the project. Quite the opposite, in fact, says Fletcher McCusker, chairman of Rio Nuevo, a nonprofit working to restore and develop historic areas of the Tucson riverfront once dominated by a landfill.

“The factions that would normally argue about this have seemed to come together on the value of the project,” he said. “So I have a pretty good feeling it’s going to happen.”

One aspect of the project that has reduced criticism, McCusker said, is the fact that much of the wastewater used for river flows will also be absorbed into the aquifer below to augment groundwater. This will help the city of 530,000 people survive future droughts, so no one can claim the water is being “wasted,” he said.

Year-round flows in the river once supported one of the largest mesquite forests in the world. Shade from those trees and the cooling effect of the river made the Tucson region a lush home for the O’odham people for thousands of years, and later a vibrant commercial center for Spanish settlers.

“This town thrived and was built on the banks of that flowing river,” McCusker said. “It’s our own damn fault that it’s not running, because we just overabused the river and the water table. To have a chance to restore it is a great idea. I’m a big fan, whether it’s a trickle or bank-to-bank.”

The city proposes to discharge as much as 3.5 million gallons per day of treated wastewater into the Santa Cruz River. The water would first be discharged at Silverlake Road. From there, it would flow north towards downtown.

The water comes from Pima County’s Agua Nueva Water Reclamation Facility, which was completed in 2014 to create a treated effluent that meets the state’s “B+” standard. It is safe for direct application to irrigate parks, golf courses and the like, and is free of nitrates and other contaminants that could taint groundwater.

Teyechea said the city expects to get a 50 percent “recharge credit” from the state for every gallon it releases to the river. This means it would be allowed to withdraw half of what it releases to the river, at a later date, from the groundwater aquifer to use in its drinking water system. The 50 percent figure accounts for losses to evaporation and vegetation.

“We don’t have to do this. We could be putting it into our recharge basin where we get 100 percent credit,” she said. “But the intent is to have nice areas where people can enjoy the river – hopefully a nice riparian area.”

City officials don’t know how rapidly the water will infiltrate into the riverbed. Therefore, they don’t yet know how far the river will flow once it gets water back.

As a result, a second phase of the project is planned to release more recycled water into the river further downstream at Cushing Street, in the heart of downtown, just a few blocks from the Tucson Convention Center. This would ensure river flow all the way through the city’s urban core.

Once flowing again, the river is expected to help grow back some of the mesquite forest that once provided so much shade in Tucson. It should also attract legions of birds, amphibians and other wildlife.

And, of course, it’s likely to draw people back to the Santa Cruz River, the original hub of life in Tucson.

“There’s a lot of interest now in restoring this as Tucson’s place of origin,” McCusker said. “So hopefully this is part of the spark. And it’s kind of energized the whole community to not only restore the river, but to restore its ancient origins as a park. We’re all trying to work in that direction.”

The city expects to have water flowing in the river again by Memorial Day in 2019.