Looking to provide secure, sustainable water resources through the rest of the century, the City of Tucson, Arizona, is pursuing a holistic approach to water management. As outlined in the recently released draft version of its One Water 2100 Plan, Tucson Water intends to build upon its ongoing process of diversifying its water supplies and managing demand. Amid such looming uncertainties as climate change, population growth, and potential cuts to its critical water supply from the Colorado River, Tucson Water has developed a series of strategies and actions designed to make the city a “sustainable oasis” in the Sonoran Desert.

New approach

Released on May 26, the draft plan, which can be downloaded here, entails the first new comprehensive plan by Tucson Water since 2004. It is also the first to propose the use of a One Water approach, says Jaimie Galayda, the lead planner for conservation and stormwater resources for Tucson Water. “One Water is definitely a new approach [for Tucson Water] and this is the first time we've taken it with a long-range plan,” Galayda says.

The plan’s One Water focus reflects a desire on the part of the utility’s management to pursue a holistic approach to water resources, Galayda says. The leadership of Tucson Water feels “strongly about the importance of that integrated approach to water resource management,” she says. “It was at their direction that we took this approach for the long-range plan.”

Challenges and opportunities

Once completely dependent on a nonrenewable groundwater source, Tucson has diversified its water supplies in recent decades, improving the sustainability of the desert city’s water resources. 

As of 2020, 82 percent of the city’s water supply was delivered from the Colorado River by the Central Arizona Project (CAP), the 336-mile long system of aqueducts, tunnels, pumping stations, and pipelines that conveys water from Lake Havasu to the Arizona counties of Maricopa, Pinal, and Pima. 

Thanks in large part to its previous conservation efforts, Tucson Water has been able to store portions of its CAP water underground in aquifers, where it can be recovered for later use. Stored water that is not retrieved represent “storage credits” that Tucson may draw on in the event of future supply reductions. In fact, two decades of drought have decimated water levels on the Colorado River, prompting cuts to the CAP and raising fears of further supply reductions in the future.

Another 12 percent of Tucson’s supply comprised recycled water, while the remaining 6 percent consisted of what the city calls “remediated groundwater,” or groundwater that is treated to remove certain contaminants before entering Tucson’s recycled water system.

A key focus of the draft One Water plan includes continued efforts to diversify Tucson’s water sources. As part of its scenario planning process that it used to develop the draft plan, Tucson Water “identified key vulnerabilities and opportunities for water supply portfolio diversification and demand management,” the plan states. “Supply vulnerabilities include over-reliance on the Colorado River, and the potential for the reduction of available water within each of the existing renewable water supplies due to drought, climate change, and other factors.” 

As for future water demands, key vulnerabilities “include population growth, land use changes, and economic factors,” according to the plan. Tucson Water predicts that its customer base will increase by 29 percent, or about 213,000 people, by 2100, to an estimated total of 947,000. 

To further diversify its water supply portfolio, Tucson can increase the “use of locally controlled and distributed sources, such as recycled water and rainwater and stormwater harvesting,” the plan states. On the water demand management side, opportunities include “developing and implementing a consistent and effective public outreach and education campaign to build on Tucson Water's strong existing water conservation programs,” the plan notes. 

Four scenarios

The foundation of Tucson’s draft One Water plan rests on four future scenarios for the city that Tucson Water identified using future population and long-term potable water use projections through 2100.

“Each scenario considers a different combination of water demand and water supply portfolio assumptions,” the plan states. “The key water demand variables are gallons per capita per day and population growth. The key water supply variable is the City's allocation of Colorado River water.”

This focus on water supply variability and demand management reflects the fact that these two issues “rose to the top as the two major areas of concern” of the public, Galayda says.

The four scenarios comprise a matrix aligned on two axes: a vertical axis ranging from increased diversification to decreased diversification of the city’s water supply portfolio and a horizontal axis ranging from decreased water demand to increased water demand.

The four resulting scenarios represent the outcomes of potential future choices made regarding water supplies and demand:

• Sustainable Oasis, which results from increased supply diversification and decreased water demand

• Desert Oasis, the result of increased supply diversification but increased water demand

• Counting Buckets, following a decrease in supply diversification and a decreased water demand

• Thirsty Desert, a combination of decreased supply diversification and increased water demand.

Tucson Water projects that it will have “sufficient supplies to meet demand through the year 2100” under all four scenarios, according to the plan. “Under the Sustainable Oasis scenario, Tucson Water would be able to meet demands with renewable supplies and continue storing CAP water underground for future use. Under the Thirsty Desert scenario, storage credits are needed to meet future demand and Tucson Water begins to rely on groundwater resources again.”

Sustainable Oasis

Tucson Water is setting its sights on achieving the Sustainable Oasis option. The utility “will use the strategies described in the Plan to avoid the risks of the Thirsty Desert scenario and work towards the Sustainable Oasis future where the water supplies are diverse, locally controlled, and water demands are well managed,” the plan states.

“We show that if we're able to drive down our [gallons per capita per day] and only get a relatively limited cut to our Central Arizona project allotment, we would be able to continue meeting our long-range demands with that renewable resource,” Galayda says. “We definitely want to maintain as diversified a supply portfolio as possible and keep saving water in the ground as long as possible.”

Another key goal involves avoiding a return to an over-reliance on groundwater, Galayda says. “We would definitely like to avoid going back to the time when we were completely reliant on groundwater, as it is a limited resource,” she says. “That is not the future we are trying to work toward.”

Strategies and actions

The draft plan includes 16 “high-priority strategies” and 66 “implementation actions” intended to help ensure that Tucson appropriately diversifies its water supply portfolio and adequately manages demand. In the plan, Tucson Water notes the relative priority, expense, and level of effort associated with each strategy.

Three of the strategies concern surface water:

• Maximize the benefits of current Colorado River water.

• Work with the State of Arizona to explore additional water supplies for CAP.

• Advocate for Tucson’s allocation of Colorado River water through the CAP in state and federal negotiations.

Another three strategies pertain to groundwater:

• Partner with regional water organizations to protect the aquifer.

• Accelerate groundwater cleanup efforts to make local supplies more available.

• Explore and invest in new treatment technologies to address unregulated, emerging water quality issues.

When it comes to recycled water, the draft plan calls on Tucson Water to pursue the following strategies:

• Adopt new policies for water reuse in buildings.

• Begin purifying recycled water to drinking water standards.

• Implement treatment technologies to address unregulated, emerging water quality issues.

For the final set of strategies related to water supplies, Tucson Water will “explore opportunities for large scale stormwater projects with multiple benefits” and “integrate and align stormwater standards, policies, and practices across the region,” the plan states.

On the demand management side, strategies include improving outreach for low-income assistance programs for homeowners and renters and increasing water savings opportunities through incentive programs for residential and commercial customers.

Other strategies entail installing “smart meters” to monitor water use in real time, conducting research on new technologies and approaches for water conservation, and providing landscape training to reduce outdoor water use.

Moving forward

Multiple consultants have assisted Tucson Water in the development of the draft One Water plan. Carollo Engineers, Inc., provided project management support and technical support. The consulting firms Jacobs and HDR also provided technical support, while Katz & Associates, Brown and Caldwell, and the Gordley Group conducted public engagement and scenario planning.

Public comments on the draft plan are due by July 21. Tucson Water will incorporate public feedback and prepare a revised version to present to the mayor and city council in August, in advance of a September meeting on the plan, Galayda says. 

Ultimately, the goal is to finalize the One Water plan by mid-November, Galayda says, when the U.S. Water Alliance is scheduled to hold its annual One Water Summit in Tucson.