Careful management of our water resources is critical to Tucson’s long-term sustainability. One Water is a new approach for managing water resources for long term resilience and sustainability, meeting both community and ecosystem needs. This approach treats all water resources as equally important. Here in Tucson, our water resources are surface water, groundwater, recycled water, and rain and stormwater harvesting, as shown in Tuscon’s historical water production graph.
Decades of proactive planning and policy making have increased our supply diversity, groundwater savings, and aquifer levels. Renewable Colorado River water delivered via the Central Arizona Project is our primary source of drinking water. This water is recharged in Avra Valley and recovered through wells. Because our consumption levels are low, we save a third of our Colorado River water allotment every year. Our additional access to our groundwater supplies will last for several decades.
Tucson was one of the first communities in the country to reduce potable water consumption with a reclaimed system. Recharged recycled water provides yet another back up to Colorado River water supplies. Using harvested rain and stormwater to irrigate trees and plants increases our ability to adapt to climate change and further reduces our demand for both Colorado River water and reclaimed water. Tucson Water’s diverse water supply portfolio and groundwater savings makes Tucson the most water resilient City in the Southwest.
A common way to measure demand for water utilities is gallons per capita per day (GPCD). Tucson’s overall GPCD has consistently been among the lowest in the Southwest. Tucson has a relatively low GPCD due in large part to our conservation program which got started in the early 1970s. Conservation programs seek to promote more efficient use of existing water resources. Tucson Water offers rebates for high efficiency toilets, washing machines, and urinals. Training opportunities and incentives for using water more efficiently in our landscapes are also available.
Here is a link to the Tucson My Water Quality Map.
This graph shows the evolution of Tucson’s water supply dating back to the 1940s. In the mid-80s, Tucson Water began to diversify its supply beginning with recycled water and then adding groundwater storage in the 90s. Stormwater capture is a small, but growing source of today’s portfolio.
Tucson Water’s share of Colorado River water is just over 144,000 acre feet per year (an acre foot is enough water to fill an acre of land to the depth of one foot). Tucson began receiving Colorado River water via the Central Arizona Project (CAP) canal in the 1990s. This renewable, surface water source goes through a process known as recharge and recovery. There are large, shallow basins at delivery points along the canal in Avra Valley and just south of Tucson. When Colorado River water fills these basins, it infiltrates the pores between bits of sand and rock and eventually settles down on top of the aquifer. This is known as groundwater recharge. The amount of water needed to satisfy customer demand is pumped back out through wells during the recovery process.
Like any other surface water resource, the availability of Colorado River water depends on precipitation, especially snow-pack, in the Colorado River watershed. Drought has impacted the amount of snow pack in the Rockies and water in the Colorado River. Tucson Water’s Drought Preparedness and Response plan describes how our allocation of Colorado River water will be impacted and how we will respond.
This map shows how surface water from the Colorado River delivered through the Central Arizona Project canal is recharged and recovered, then distributed throughout Tucson Water’s service area.
Before the early 2000s, Tucson was the largest metropolitan area in the United States completely dependent on groundwater. Recovered Colorado River water now supplies the vast majority of our drinking water needs. This shift can be seen in the water production graph above.
Groundwater is considered a finite water resource because the aquifer developed on a geologic time-scale and does not receive much natural recharge each year. In contrast, Colorado River water delivered through the CAP is considered a renewable resource because it is fed by snowmelt each year and replenished in a human timescale.
The Arizona Groundwater Management Act was established in 1980 to better manage groundwater withdrawals. This law laid out the Assured Water Supply (AWS) rules, which govern the amount of groundwater that all water utilities can pump or produce with wells. Ever since Tucson Water transitioned to renewable water supplies, aquifer levels have been rising in some areas, especially in the vicinity of the Avra Valley recharge and recovery projects. This was the main goal of the Groundwater Management Act, to balance groundwater recharge and withdrawals.
This map shows the approximate volumes of water stored in Tucson’s aquifers, which now hold enough water to serve residents for decades.
Recycled water resources in Tucson include both reclaimed and gray water. Reclaimed water is wastewater that has been treated to high quality standards and is used primarily for irrigation. Gray water comes from sinks (other than kitchen sinks), showers, baths or, washing machines and can also be used for irrigation. Using reclaimed and gray water for irrigation reduces the demand for drinking water, allowing us to stretch our renewable water resources further out into the future.
In 1984, Tucson was one of the first cities in the country to begin recycling water by treating wastewater for irrigation and other non-potable water uses. The first customer was a golf course, but now the reclaimed system serves the vast majority of parks, schools, municipal properties (via Intergovernmental Agreements or IGAs), and golf courses throughout the region in addition to some residential customers.
Demand for reclaimed water increases during the hotter, drier summer days. This is known as the peak-demand period. Tucson Water’s reclaimed system reaches capacity during the peak-demand period, but it has excess capacity during the winter months. Reclaimed water produced during the off-peak period that isn’t being used by customers is used to replenish the aquifer through recharge projects like the Southeast Houghton Area Recharge Project, Santa Cruz River Heritage Project, and the Sweetwater Recharge Facility.
Recycled water flows through purple pipe. This map shows where recycled water flows to serve irrigation needs for parks, golf course and other public open spaces.
Rain and stormwater harvesting are a small but growing component of Tucson’s water supply. Although it is unmetered, the estimated amount of rain and stormwater collected is represented by the green line on top of the water production graph.
There are two general categories of rainwater harvesting; active and passive. Active rainwater harvesting refers to a tank or cistern storing rainwater collected from roofs, which provides a means to store the rainwater for later use. Passive rainwater harvesting refers to directing and retaining water in the landscape using site appropriate practices such as basins, berms, terraces, swales, and infiltration trenches.
Stormwater harvesting refers to rainwater collected from non-roof surfaces, such as streets, parking lots, hardscapes, and landscapes. Strategies to capture and utilize this water include landscaping design to retain water in soil, semi-porous hardscape material, curb cuts, and detention/retention basins.
For more information on Storm to Shade, please visit the City of Tucson’s Green Stormwater Infrastructure program website .
Stormwater is the latest addition to Tucson Water’s diversified resource portfolio. It is being used to increase tree canopy and supply green infrastructure sites in the City’s right of way.
Copyright © 2022 City of Tucson
