Tucson OKs building toilet-to-tap-water plant with federal money

The Tucson City Council has approved plans to build a toilet-to-tap-water plant with up to $86.7 million in federal funds.

Mayor Regina Romero and councilmembers accepted the agreement, negotiated by Tucson Water and the U.S. Bureau of Reclamation, to build the plant by a 7-0 vote Tuesday night.

Under the agreement, the bureau will pay the city up to $86.7 million to build the “advanced water purification direct potable reuse demonstration facility” before 2032.

Once finished, the plant will convert about 2.5 million gallons a day of treated wastewater from the Pima County-run Tres Rios wastewater plant into drinkable water, the Star previously reported.

That 2.5 million gallons represents between 2% and 5% of the city’s total drinking water supply, Tucson Water Director John Kmiec said.

Councilman Kevin Dahl called it a “monumental agreement that will provide a new source, from an old source, of potable, drinkable water.”

“Desert cities need water from every single source, and I wanted to point out that this is available to us because Tucson does so much water conservation,” Dahl said. “That has allowed us to make some money, selling back the water to other users, and in this case we’re trading water for new infrastructure.”

“Water conservation is key. As we negotiate for things, we need to negotiate for more water conservation. There’s more we can do,” said Dahl.

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In return, Tucson is agreeing to leave about 56,000 acre-feet of its Central Arizona Project water supply from the Colorado River in Lake Mead over a decade.

The CAP water savings the city is accepting in return for money to build the wastewater plant will be on top of 110,000 acre-feet of CAP water Tucson already agreed to leave in the lake in calendar years 2023, 2024 and 2025 in return for additional compensation.

Another part of the agreement approved Tuesday night puts the city on the hook for leaving another 50,000-acre feet of CAP water in the lake in return for another $20 million in federal funding.

A northwest-side area was chosen for the plant location in part because those residents have lost a major portion of their local supply due to the shutdown of a number of drinking wells in that area due to contamination by the “forever chemicals” known as PFAS compounds.

For that reason, in November 2023 the Environmental Protection Agency invested $30 million into building a second water treatment facility for northwest-Tucson water wells, after city officials began testing them a few years prior and identified more than two dozen wells that had to be shut down due to PFAS chemicals found in the water.

The city’s One Water long-range water plan, adopted about a year ago, called for the utility to build small, pilot wastewater-for-drinking projects as a possible preview for building a larger plant to serve water for more people.

Currently, recycled wastewater from the Tres Rios plant is dumped into the Santa Cruz River, where it eventually leaves the Tucson area by flowing downstream into Pinal County, Kmiec said.

Around the West, many cities including Phoenix and Scottsdale now are actively studying or planning to build wastewater-to-drinking plants as a way of replacing other supplies such as groundwater and Colorado River water that have diminished in recent years due to drought and over-pumping.

The northwest-side facility is possible in part because the Arizona Department of Environmental Quality adopted regulations last year that authorize local entities to treat wastewater for drinking through a method known as “direct potable reuse.”