A water supply used for suburban Arizona growth is at risk

The water in question is called NIA water, and it has made up more than 20% of the CAP’s historic total supply. It was formerly called non-Indian agriculture water because it used to be delivered to farmers.

But as CAP water rights were gradually transferred from farmers, the NIA supplies found their way to cities, mines and other industries, tribes and other entities.

Now that supply is in jeopardy as water negotiators for the seven Colorado River Basin states grapple over how to cut their water use to keep the declining river from ever drying up.

“That (NIA) water is gone,” Arizona Department of Water Resources Director Tom Buschatzke told a Colorado River conference in Boulder on Thursday. 

He was looking ahead to how the basin states will carve up the river’s diminishing supplies for a new operating agreement.

That raises questions about how the Central Arizona Groundwater Replenishment District can meet future legal obligations to recharge renewable CAP water into aquifers to compensate for groundwater pumped for many suburban subdivisions in growing areas near Phoenix and Tucson and in Pinal County.

Under state law, developers of new subdivisions in those areas must prove they will have an assured, 100-year water supply for them to be built. If that supply is to be pumped groundwater, the replenishment district must find renewable water supplies such as CAP water to put back into the aquifer to compensate for what’s pumped. Until now, the district has always been able to find such replenishment supplies since it began operations in the middle 1990s.

A February 2024 document, outlining how the district plans to obtain renewable supplies for the period covering 2025 through 2044, shows a major reliance on NIA supplies to meet replenishment obligations. Showing where the supplies will come from is a key element of the district’s next plan of operations that would cover the same period. The plan must be submitted to the Arizona Department of Water Resources for approval.

But at this time, agency officials don’t have answers to questions about how cutbacks of the NAI supply could affect its future activities.

In fact, it’s not clear when the board will even vote on a proposed plan, CAP Board President Terry Goddard told the Arizona Daily Star on Friday.

Despite Buschatzke’s comment, Goddard said he’s not ready to completely write off hopes of getting NIA supplies in the event of future good water years.

But when asked how confident he is of finding replacement supplies if that becomes necessary, Goddard replied, “That’s the $64,000 question, and I can’t really give you a high degree of confidence. The nature of this particular situation is one of water scarcity. That’s behind our questions about this.”

While possible future replacement supplies clearly exist to meet the district’s recharge needs, “obviously, any dependable replacement supply is going to be a difficult to find,” he said.

The district recharges CAP supplies in Maricopa, Pima and Pinal counties for developments built in areas not served by a water utility such as Tucson Water or the city of Phoenix that have formal state designations of having an assured, 100-year water supply.

Developments served by this district tend to be in farther-flung suburban areas such as the unincorporated communities of Green Valley, Quail Creek and SaddleBrooke near Tucson, and fast-growing Phoenix-area suburbs including Buckeye and Queen Creek.

The likely disappearance of the NIA supplies came into public view on Thursday, at the annual Colorado River conference in Boulder, sponsored by the Getches-Wilkinson Center for Natural Resources and the Environment.

There, Arizona water chief Buschatke said the NIA water will go away, based on “the numbers we negotiated” among the three Lower Basin states to reduce river water use to wipe out a longstanding “structural deficit” between use and supplies. To eliminate that deficit, the three states — Arizona, California and Nevada — have already agreed to trim their river water use by 1.5 million acre-feet a year — about 20% of the Lower Basin’s annual river water supply.

On Friday, ADWR spokeswoman Shauna Evans said NIA water supplies would be eliminated starting in 2027, if the seven river…