A proposed deal to cut Colorado River water deliveries to Arizona and two other Lower Basin states wouldn’t cause an immediate water crisis, but could bring problems farther down the road.

It would leave plenty of water for immediate use for Tucson, Phoenix and other cities serving drinking water from the river via the Central Arizona Project. But it would reduce the amount of unused CAP water cities can store to prepare for a drier future. It would also crimp the use of CAP by farms — for whom the project was originally designed back in the 1950s and ’60s.

Under the proposed agreement, Arizona could lose about 13 percent of its CAP supply as early as next year, depending on how long it takes for the three states to reach agreement and to sell the deal to officials inside the states. If Lake Mead keeps dropping as it has done the past 16 years, the state could gradually lose as much as 40 percent of its CAP supply. But these cuts would bolster lake levels enough to forestall even deeper cuts later, authorities have said.

It’s not clear today how cities, farms and other users would share the cuts, or for how many years the cuts would last. But Arizona Department of Water Resources Director Tom Buschatzke hopes to strike a “grand bargain” among various users on how they’d be divided.

Given the big value that economists and others have placed on the CAP — a study done for the project a few years back pegged its worth to the economy at 300 times the cost cities, farms and others pay for the water — a major cutback in CAP deliveries would be an economic hit, said CAP General Manager Ted Cooke and the head of the U.S. Bureau of Reclamation, which manages the reservoirs where river water is stored. But it’s less of a hit than the state and its economy would take if Lake Mead levels were allowed to keep dropping without additional management, said Estevan Lopez, the bureau’s commissioner.

And, because Arizona cities and the state as a whole are storing so much CAP water now, their water systems wouldn’t suffer immediately. Some, including Tucson, could survive a 40 percent cut for years without a pinch, officials say.

But when less water is delivered, cities and farms would pay more per gallon to meet CAP’s fixed costs, such as maintenance and staff. No one knows exactly how much more, but Tucson officials say CAP has measures in place to limit rate shock.

Farmers would lose a good deal of water immediately, although they hope to survive by striking a deal with cities, perhaps by having cities pay farmers to be more water-efficient to free up some of their water.

Politically, the prospect of a part-empty CAP canal would likely trigger a push for expensive desalination of brackish groundwater or seawater. That’s a controversial move, partly because of the highly saline wastewater to be discharged into the ocean afterward. It also would force Tucson and other municipalities to consider other solu-tions, such as recycling wastewater to drink and capturing stormwater in large basins.

Tucson doing OK

Tucson Water already is more prepared than most if not all Arizona cities to deal with CAP cutbacks.

That’s not due so much to brilliant planning as to the utility’s botched introduction of CAP water in the early 1990s. Due in large part to Tucson Water’s failure to listen to consultants who urged it to thoroughly test the CAP’s impacts on existing plumbing in advance, the utility sent out corrosive water that rotted and rusted the water system’s aging pipes.

That sent a flood of brown and rusty colored water into living rooms. It led to the shutdown of the CAP in Tucson for nearly a decade, and to a 1995 referendum banning the direct delivery of CAP to Tucson in favor of recharging it into the ground.

Chastened, Tucson Water officials decided a few years later on a series of elongated, rectangular recharge basins to put CAP water in and take it right back out. Starting in 2001 and through the next decade, the city spent $250 million to build 550 acres of basins in central and southern Avra Valley, and to install wells and pumps needed to get the water out.

Today, the city pumps water from these basins to meet most of its annual demand. It already stores about 300,000 acre-feet — three years’ worth — at the Avra Valley basins and at another series of basins by Pima Mine Road south of Tucson.

It sets aside another one-third of its annual, 144,000 acre-foot CAP allocation. Since it only uses two-thirds of its annual supply, and has another 10,000 acre-feet of treated contaminated water available annually from the south side, the city can take a 40 percent CAP cut without having to pump more groundwater, Tucson Water Director Timothy Thomure said.

Conservation has also helped, he said. In 2015, Tucson used about 40,000 acre-feet less water total than in 2006, and today uses about the same amount of water as it did in 1980 even though the utility serves about 300,000 more people, said Wally Wilson, Tucson Water’s lead hydrologist.

“If we hadn’t had the conservation results that we’ve we seen, we would be at more risk during a shortage than we are today,” Thomure said.

Others recharge, too

Oro Valley, Metro Water and other northwest-side water users with CAP rights also recharge much of their water into large basins along the lower Santa Cruz River.

They plan to spend about $36 million to build 13 miles of pipeline, wells and other infrastructure to deliver that water directly to their customers by the early 2020s. Today, they use CAP water stored underground as credits, allowing them to pump groundwater elsewhere.

In the meantime, they say they are prepared for shortages because they’re not using their entire allocations. Metro says it can take a 40 percent cut without having to pump additional groundwater, and Oro Valley says it wouldn’t have to pump more groundwater for at least 15 years.

Phoenix also could sustain a 40 percent cut because it’s taking only two-thirds of its CAP allocation and gets 55 to 60 percent of its water from the Salt River Project, said Kathryn Sorensen, the Phoenix water utility’s director. Phoenix is starting to store some of its unused CAP water in Tucson’s recharge basins, on the premise that Tucson can take that water during shortages and Phoenix can take some of Tucson’s CAP deliveries.

“We’re far from feeling overly anxious or from any panicking because of the preparation that we’ve done,” said Warren Tenney, director of a water users group representing Phoenix and nine other Maricopa County cities.

Part of that preparation is the state-run Arizona Water Bank, which puts CAP water into the ground each year for use during future shortages. It has recharged nearly 4 million acre-feet of CAP water at 25 facilities — including eight in the Tucson area — since the late 1990s. Most of that is for Arizona cities, tribes and other users, including 422,000 acre-feet for Tucson and its suburbs. About a quarter is for Nevada, which would exchange it for some of Arizona’s water from Lake Mead during shortages.

But except for some of the Tucson-area recharge facilities such as the city’s Pima Mine Road site, the water bank has no pumps, pipelines or wells to get the water out. The CAP, the state Department of Water Resources and Phoenix-area cities are studying how to get access to that water — at a high cost or considering an exchange for groundwater stored elsewhere that is easier to pump out.

Farms would suffer significant losses under current water-shortage guidelines, said Paul Orme, an attorney for four Central Arizona irrigation districts. But the new agreement may require them to take bigger cuts early. For the water they lose, “We would look to getting some financial consideration help with developing more groundwater supplies, water conservation, invest-ment in drip systems, that kind of thing,” he said

That could work, said University of Arizona law professor Robert Glennon, who has written a report on how to help farms cope with coming water shortages by selling and/or trading rights to urban areas.

He sees this as a way to protect rural communities by helping farms grow the same amount of goods but using less water.

Looking at the entire West, he has calculated that if farms are paid to reduce their consumption by just 4 percent, that frees enough water to increase municipal and industrial consumption by 50 percent — far more than they need.

“There’s not a farmer in the West who can look me in the eye and say we can’t achieve that,” said Glennon, author of two books on water. “I don’t blame the farmers. It’s their water. If cities want farmers to change, they need to give farmers a reason to change.”

More cuts possible

A 40 percent CAP cut may not be the largest Arizona ever has to take. The agreement under discussion would last until 2026, and cuts in deliveries might increase if climate change reduces the river’s supply further.

But CAP General Manager Ted Cooke said he believes Arizona will quickly replace the Colorado River water it loses. The agency will expand its exploration of removing salt from brackish groundwater in Arizona and seawater off the coasts of Mexico or California.

“The value of water is so high in Arizona, we’re not going to sit back and say, ‘That’s just the way it is’ that we’re losing it. That magnificent canal will be partially empty and we’ll still be paying for it,” he said.

“It may take 20 years for the water we lose to be replaced by another source, but I’m convinced we’ll do it.”

Tucson Water’s Thomure also supports considering desalination as part of an “all of the above” water-supply strategy that includes treating wastewater to drink, large-scale stormwater capture and rainwater harvesting by homeowners.

Cooke and Thomure say the costs of desalination already are being cut by better technology, and that those costs will look even better once CAP prices are driven up by shorter supplies. Thomure also says desal plants can be better designed to avoid hurting aquatic life.

Critics, however, note that the White House has said the cost of desalinating seawater would have to drop by four times to make the price competitive with conventional water treatment.

“It is interesting that they say we will take a hit economically with the shortage, but then go on to talk about desalination. Talk about an economic hit,” said Sandy Bahr, director of the Sierra Club’s Grand Canyon Chapter. “We would object to it as it is expensive, energy intensive, and leaves behind brine that cannot be disposed of effectively. We do not think just dumping it in the ocean is a good option. They seem to forget that the oceans are also being affected by climate change and what we are already dumping in them.”

Maybe, she said, it’s time to talk instead about whether it makes sense to keep growing alfalfa in the desert or whether we should consider new ways to conserve water first.

“What about the exemptions for mines to the Groundwater Management Act requirements to reduce pumping? How about we look at paying the real cost of water?” Bahr asked. “A system that makes water available for basic human needs, leaves water for nature and charges a lot more for all other uses should be considered.”

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987.