Tucson, Arizona, could face a major water challenge if Lake Mead falls to “dead pool” levels preventing water from flowing downstream through Hoover Dam. However, the city’s extensive underground water reserves could help protect its residents from an immediate supply crisis.
According to a report published by WorldAtlas on October 27, 2026 Lake Mead’s water level reached 1,037.16 feet on October 22, its lowest recorded level leaving it approximately 142 feet above dead pool. At that point, the reservoir’s surface would fall below Hoover Dam’s lowest outlet gates preventing water from being released downstream by gravity.
Tucson receives Colorado River water through the Central Arizona Project (CAP) a 336 mile canal that transports water from Lake Havasu to communities across Arizona. The water is pumped uphill and delivered to Tucson, where it supplements the city’s groundwater supply.
Arizona faces significant reductions in its Colorado River allocation because of the river’s declining supplies and the priority system governing water distribution. Under the proposed 2027 Lower Basin arrangement, Arizona’s share could be reduced by approximately 760,000 acre feet or 27% of its 2.8 million acre foot allocation.
Tucson’s preliminary 2027 CAP water order is around 71,000 acre feet less than half its 144,191 acre foot allocation. A conservation agreement would leave approximately 50,000 acre-feet of the difference in Lake Mead.
The report explains that Arizona’s canal deliveries could face further pressure because California has senior water rights under the existing allocation framework. Consequently, Tucson and other Arizona communities could experience reductions well before Lake Mead reaches dead pool.
Tucson has developed a water storage system designed to reduce dependence on immediate Colorado River deliveries. Since the 1990s the city has stored treated CAP water underground allowing it to be recovered later through wells and blended with naturally occurring groundwater.
The Central Avra Valley Storage and Recovery Project and the Southern Avra Valley project use recharge basins west of the Tucson Mountains to replenish the aquifer.
According to the report approximately 78% of Tucson Water’s current deliveries come from recovered supplies stored underground. The city has also banked around 600,000 acre feet of CAP water since 2000 with an additional 400,000 acre feet or more potentially accessible through the Arizona Water Banking Authority.
Together these reserves could provide at least 10 years of supply if CAP deliveries were completely interrupted according to the report. Tucson plans to begin using stored credits to cover a projected shortfall in its 2027 water order.
Groundwater and recycled water remain important
Tucson also maintains a central well field for peak demand and emergencies. The report estimates that the groundwater available to Tucson Water, including stored and recoverable supplies, totals approximately 4.7 million acre feet.
Water conservation has further strengthened the city’s position. Average drinking water use per person fell from approximately 165 gallons a day in 2000 to 110 gallons in 2024.
Reclaimed wastewater also plays a significant role. Tucson has supplied treated wastewater to nearly 1,000 customers since 1984 including golf courses and school playing fields reducing demand for drinking water by around 4.7 billion gallons annually. This supply could continue even if Colorado River deliveries stopped.
Farmers and neighbouring communities could also be affected
A prolonged cutoff would have consequences beyond Tucson. Agricultural areas around Marana and Avra Valley depend on CAP water for irrigation while Oro Valley expects a reduction in its Colorado River supply beginning in January 2027.
The Tohono O’odham Nation’s San Xavier and Schuk Toak districts also hold CAP water rights under a settlement agreement. Disruptions to the canal could therefore affect agricultural operations, neighbouring communities and Indigenous water users.
Lake Mead’s decline highlights the growing challenges facing communities that depend on the Colorado River. Although Tucson’s underground reserves and conservation measures provide a buffer against shortages, those safeguards depend partly on storing water before supplies become unavailable.
The report notes that even the Bureau of Reclamation’s dry side forecast keeps Lake Mead more than 85 feet above dead pool through September 2028. However, the projected decline below the 1,025 foot threshold could trigger more stringent drought measures in Tucson.
The city’s experience demonstrates how long-term water banking, groundwater management, conservation and wastewater recycling can help communities prepare for prolonged drought. Yet if Colorado River supplies continue to shrink protecting these reserves and reducing demand will remain essential to Tucson’s water security.