ÃÛÌÒÓ°ÏñAV

Tucson’s water supply is roughly 80% dependent on Colorado River water, which is starting to dwindle. Lake Mead, the main water supply for the Central Arizona Project (CAP) is currently in a Tier 1 shortage and is projected to hit a record low in 2027 (U.S. Department of the Interior, Bureau of Reclamation, 2025).

As this shortage persists, CAP must limit the amount of water allocated to Tucson, reducing how much the city can store in its groundwater reserves. Groundwater serves as a natural, long-term, and effectively renewable storage system, provided recharge efforts keep pace with demand. It remains the most sustainable way for Tucson to maintain an independent, reliable water supply as upstream sources grow increasingly uncertain.

Without sufficient CAP water to supply the city or replenish the aquifer, Tucson’s growth will slow, water will become scarce, and the community will be forced to scramble for alternative sources.

Fortunately, there are other ways to recharge groundwater. One significant strategy is stormwater runoff collection. Like many cities, Tucson’s current infrastructure involves an extensive use of impermeable surfaces like concrete and asphalt roads and parking lots. However, with stormwater collection and an increase in green space, the city could store far more water for future use.

It’s reasonable to assume that rainwater harvesting in this manner would be ineffective due to our desert’s dry climate, but research suggests otherwise. In 2018, researchers Daoqin Tong and Courtney Crosson from Arizona State University and the University of Arizona, respectively, along with UA PhD candidates Yinan Zhang and Qing Zhong, found that the City of Tucson receives enough rainfall within the city limits each year to fully meet its water consumption, and more. Yet less than 2% of that rainwater is actually harvested and brought back into the system (Crosson, Tong, Zhang, & Zhong, 2018). This is where stormwater runoff infrastructure has enormous potential.

Stormwater retention systems collect runoff in ponds, tanks, or permeable surfaces that allow the water to be filtered into the aquifer below. Impervious surfaces found all around Tucson prevent this recharge from occurring and instead push the water to flood. With more runoff infrastructure, Tucson could decrease the amount of street flooding while also directing that water underground to the aquifer. These systems also create opportunities for greener, more attractive streetscapes.

To act on these findings and attain these benefits, I recommend the city adopt a policy requiring all new developments to include stormwater retention infrastructure, specifically permeable surfaces and onsite basins. This policy would diversify Tucson’s water supply and increase groundwater recharge rates, helping the city to become less dependent on an uncertain CAP allocation. As the city’s sustainable water supply grows, Tucson will increase its climate resilience and ultimately create room for more growth and development. While this policy may create high initial construction costs, discouraging some developers from building in Tucson, this policy would not otherwise require any direct spending from the city and would ultimately stabilize long-term living costs as water demand rises.

Without support from another water source, Tucson will struggle when CAP water continues to decline.

The city cannot continue to grow while ignoring the water crisis in the West. Tucson needs to take policy action to strengthen sustainable groundwater recharge, and one of the most effective strategies is reducing impervious surfaces and requiring stormwater runoff retention basins and permeable infrastructure in new developments.