Some suburbs of Tucson and Phoenix will struggle to find enough water to keep growing without damaging underground aquifers by overpumping groundwater, a new report warns.
This could lead to land subsidence, including ground fissures; lower water quality; and even the possibility of wells drying up.
The report from Arizona State University’s water institute also warns of potentially catastrophic financial problems for the agency that finds renewable water supplies for development in far-flung suburban areas.
That, in turn, could ratchet up already soaring rates for homeowners there.
The state’s system for insuring there’s enough water for much of the new suburban growth — in accord with the landmark 1980 Groundwater Management Act — is environmentally unsustainable and needs an overhaul, the report suggests.
The findings raise questions about how much more growth should continue in areas without renewable supplies such as Central Arizona Project water, said Kathleen Ferris, a former Arizona Department of Water Resources director and chief counsel who co-authored the report. CAP water comes to Arizona’s cities and farms from the Colorado River via a 336-mile-long canal system.
“Failure to find solutions to these problems could have devastating consequences down the road. Taking action to address them is the only way to protect Arizona’s water supplies for its current and future citizens,” said the report, prepared by ASU’s Kyl Center for Water Policy.
At issue is where authorities will find enough water to replenish aquifers in fast-growing areas of Pima, Pinal and Maricopa counties where groundwater is or will be pumped to supply new homes, because they don’t have access to CAP water.
The report focuses on the work of the Central Arizona Groundwater Replenishment District, a part of the CAP, whose job is to find the renewable supplies for those homes in the three counties. Under state law, the homes in these areas can be built only if renewable supplies can be found to compensate for the water pumped to serve them.
In the Tucson area, such development is occurring or is projected to occur over the next few decades in unincorporated areas north, south, northwest and southeast of the city. The areas include the Green Valley and Quail Creek areas south of Tucson, the SaddleBrooke area just north of the Pinal County border, and the Vail area southeast of Tucson.
Far more intense future development and pressure on water supplies is expected for Pinal County closer to Phoenix and for the Buckeye area west of Phoenix.
These supply issues could get worse if climate change continues to reduce Colorado River supplies, said Sarah Porter, the report’s co-author and director of the Kyl Center. During a CAP shortage, water earmarked for the suburban areas would be among the first supplies to be cut. So climate change will have a bigger impact on such water users than on cities with their own CAP supplies. Those cities have higher priorities for the water during shortages, Porter said.
Specifically, the report found:
- Because pumping for these subdivisions often occurs far from where renewable supplies are recharged — placed on the ground to seep into the aquifers — groundwater levels under these subdivisions are falling.
- Membership in the water district by homes needing groundwater replenishment has hit 286,000 homes statewide, including more than 24,000 in 122 subdivisions in the Tucson area. By 2024, about 383,000 homes statewide are expected to be district members, far more than previously expected, putting additional pressure on water supplies.
- The potential exists for a huge gap between the amount of renewable water that’s available for replenishing aquifers and the amount that new development will need over the next century. Statistics from the report suggest it could be up to 300,000 acre-feet a year —enough to serve Tucson for three years.
- The three-county district says there’s plenty of water potentially available for future development. But the report says the availability of these supplies is questionable.
- Various fees and assessments imposed on homeowners living in the areas served by the water district have escalated. The annual charge assessed on homes to pay for water supplies, water rights purchases and administrative costs, for instance, jumped in the Tucson area from $188 an acre-foot per home in 2000 to $738 this year. It’s expected to hit $775 by the mid-2020s.
Over the years, the three-county replenishment district has taken considerable criticism from environmentalists and others who say its practices encouraged unsustainable urban sprawl.
But the district isn’t to blame for problems outlined in the report, said Ferris, because it has carried out all that state law requires it to do: “The problem is that the statutes are too lenient.”
Responding through a spokeswoman, the water district said it won’t comment on the report specifically, because it just received it Thursday. In a statement, the district said it’s fulfilled its legal duties effectively, “demonstrating fiscal responsibility while securing a robust water supply portfolio that will be available through the mid-2030s.”
The district said it conducts thorough analyses of water supplies and costs to monitor their viability and changes. Due to leadership and oversight by its governing board, the district said, it is positioned as “a strong and stable component in the fabric of Arizona’s water policy.”
Here are details of the problems the new report says have been caused by allowing groundwater pumping for new growth away from where aquifers are recharged:
Despite replenishment, well levels fall
The law sets up a disconnect between groundwater pumping and recharge that’s “problematic.”
Because no CAP is delivered to developing areas such as SaddleBrooke and Green Valley, private water companies and other utilities continue pumping groundwater there.
To compensate for that pumping, the water replenishment district recharges aquifers in areas far away, such as the Pima Mine Road Recharge Project south of Tucson, the Avra Valley Recharge Project west of Tucson and the Lower Santa Cruz Recharge Project adjacent to the Santa Cruz River and northwest of Avra Valley Road. So the water table under developing areas keeps falling.
“When replenishment does not take place near the site of groundwater withdrawal, the replenished water will not reduce the local geological impacts of pumping and will do nothing to recharge the aquifers that CAGRD members are counting on to supply groundwater,” the report said, using an acronym for the replenishment district.
One problem is that in some of these areas, it’s highly uncertain whether even enough groundwater is physically available. Just last week, for instance, the Arizona Department of Water Resources released information showing that Pinal County has 8 million acre feet less groundwater than is expected to be demanded over the next 100 years.
An aquifer that keeps falling can trigger land subsidence, or a settlement of the ground that causes earth fissures. Groundwater quality can also worsen and pumping costs invariably rise. Once aquifers collapse from subsidence, they can’t be restored, the report said.
The biggest problem with the pumping is that it’s unsustainable, leading to eventual groundwater depletion, said the report, adding: “This grim reality leads to a crucial question: Who will provide water to homeowners and businesses on CAGRD member lands if their wells run dry?”
Since groundwater may legally be pumped to 1,000 feet below land surface in the Phoenix and Tucson areas and 1,100 feet deep in the Pinal County area, “this is not an academic question. It is a serious likelihood, with major consequences that must be considered.”
Escalating water demands
By 2114, the district expects to have legal obligations to recharge 113,000 acre feet of renewable water, nearly three times what it does today. That doesn’t account for massive growth expected in Pinal County and in Buckeye in Maricopa County.
Bold predictions, uncertain supplies
The water replenishment district says it has identified up to 980,000 acre-feet of what it calls “potentially available” supplies it expects to have access to by 2114. Even if only half that amount turns out to be realistic, that’s still far more than it expects to need by then.
But it’s questionable whether many of those supplies will be available, the Kyl Center report said.
A big chunk of that expected supply, for instance, would come from CAP water that other urban and tribal users don’t want. But that “excess” supply has rapidly diminished in recent years as cities have used more of their water. It’s expected to go away once CAP shortages get worse, the report said.
The replenishment district has also projected it could buy a large amount of Colorado River water from on-river users in places such as Mohave County.
But since then, the district has canceled efforts to buy water rights from there and from Quartzsite in neighboring La Paz County. Residents of Mohave and La Paz counties fought the plan because they didn’t want their own water supplies drained.
The district has also projected that it could buy and import groundwater from Western Arizona and buy and recharge treated sewage effluent. But those supplies both look uncertain today, said Porter.
Importing groundwater will be very expensive, in part because it may require some treatment before putting it into the CAP canal. As for effluent, “the (municipal) water providers that have effluent already have a plan for their effluent. A lot of water providers are looking to effluent as an important part of their growth portfolio,” Porter said.
The replenishment district did strike a deal last year that virtually doubled its total supply: a $95 million water rights purchase from the Gila River Indian Community that will bring the district 900,000 acre-feet over 25 years.
But about half that water has lower priority during shortages than what’s typical for Indian-owned CAP water. So “the full amount of this supply is not likely to be available every year,” the report said.
As costs escalate for homeowners and subdivisions to join the replenishment district and pay it to recharge renewable water, some water district members — subdivisions and homeowners associations — are finding cheaper alternatives.
They include two types of credits that water rights owners can buy, letting them pump groundwater and avoid having to recharge surface water to compensate for it.
With one, someone who owns a historic “grandfathered” water right can give up that right in exchange for such credits. With another, people or government entities can buy long-term storage credits from others who have recharged CAP water or effluent into the ground. That gives the purchaser the right to pump groundwater.
If these practices continue, declining customers for the water district could force rates to rise further, triggering a painful cycle of rising rates and declining customers, said Ferris. The ultimate result for the district could be catastrophic financially.
The Arizona Department of Water Resources, which enforces the 1980 groundwater law, won’t comment until it reviews the report, a spokesman said.
Southern Arizona Home Builders Association President David Godlewski said the link between the groundwater replenishment district and Arizona’s economy is “undeniable,” and that “everything in our power must be done, including acquisitions of additional water resources, to protect and enhance it.”
Efforts to change or weaken it pose serious economic risks, said Godlewski, adding that without the district, “new economic development, as well as the existing economy in Tucson, would be adversely impacted.”
The CAP said it wants to be part of the discussion about appropriate growth, but “it may not be the appropriate agency to lead it because the focus of this debate would go beyond its legal responsibilities,” it said.
Kathy Jacobs, who helped write the 1993 rules to assure Arizona’s growing areas have water supplies for 100 years, called the report “excellent, very well researched and documented.” She agrees with all but one of its recommendations.
She has reservations only about its proposal to require that all pumping of groundwater be done in the same places where recharge occurs. Exceptions to such a rule should definitely be allowed, she said. An example includes recharging water away from pumping areas to restore riparian habitat.
There were practical reasons for creating the groundwater replenishment district, “but with the benefit of hindsight it is clear that certain components of the Assured Water Supply program need to be tightened up,” said Jacobs.
One oversight in past water management, she said, has been its failure to fully acknowledge, until recently, the implications of climate change and the chronic overuse of the Colorado River.
University of Arizona law professor Robert Glennon, who has written two books about water supply issues, gave the report high marks.
“The CAGRD (water district) has been a house of cards from its inception. Facing the problems with it is long past due,” Glennon said. “I hope our legislators, the Governor’s Office, the Department of Water Resources, and the CAP district pay close attention to the findings in this report and take swift action.”
Contact reporter Tony Davis at
firstname.lastname@example.org or 806-7746.