What is Scottsdale’s wastewater swap plan, and will it work?

SCOTTSDALE, AZ (AZFamily) — Scottsdale has proposed sending its treated wastewater into the Central Arizona Project (CAP) canal in exchange for a share of another community’s CAP water, as Arizona faces major cuts to Colorado River supplies.

Sarah Porter, director of the Kyle Center for Water Policy at Arizona State University’s Morrison Institute, said the proposal surprised her.

“This one, I hadn’t seen coming,” Porter said.

Under the plan, Scottsdale would take some of its advanced purified water, which is recycled wastewater treated at a city plant, and trade it to another community for a share of that community’s Central Arizona Project water. The city would pump the treated water directly into the canal system to complete the swap.

Porter said the water Scottsdale would put into the system is pure and exceeds applicable drinking water standards.

“It’s unusual to want to put water that you’ve already spent so much money on back into a system that has a lot of untreated water,” Porter said.

Scottsdale’s reliance on the Colorado River

Porter said Scottsdale is one of the cities that relies most heavily on the Colorado River, with about 70% of the water that reaches customers’ taps coming from a plant that runs on Central Arizona Project water.

“What Scottsdale faces now is they have limited choices,” Porter said.

In its proposal, city officials acknowledged the lingering stigma of reusing treated wastewater, writing that the city would “propose compensating downstream users.”

Thyra Ryden-Diaz, interim senior director of Scottsdale Water, said the proposal is a starting point.

“Our proposal is really a white paper,” Ryden-Diaz said.

Ryden-Diaz said more than 500 utilities already discharge treated wastewater into the Colorado River and its tributaries. She said the water Scottsdale would put into the system is cleaner than that and could improve water quality in the CAP system.

“Our water is super clean,” Ryden-Diaz said. “It’s drinking water standard. It’s not what we’re getting from Vegas.”

Downstream approval remains a question

Porter said getting sign-off from everyone downstream may not be simple or cheap.

“There’s some additional expense in terms of making everybody downstream happy,” Porter said. “And that’s a lot of people.”

The plan is not finalized and would require an agreement from the Central Arizona Project. Central Arizona Project officials confirmed they received the proposal last Friday from Scottsdale and will be reviewing it.

Why not send the water straight to taps?

Ryden-Diaz said Scottsdale does not currently have the permit needed to put the treated water directly into the drinking water system, in line with many municipalities.

That is why the city is proposing the trade, pumping the water into the canal in exchange for water it can already treat and deliver to taps.

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