The widespread concern about Arizona “running out of water” is better understood as a challenge of resource management under severe climate stress. The state has developed a complex and diverse water portfolio, but this system is now being tested by the prolonged megadrought affecting the Colorado River Basin. The risk of taps going dry for major metropolitan areas remains low due to layers of protection. However, the current crisis requires sophisticated adaptation and strict adherence to established legal priorities. Arizona’s path forward involves balancing a finite supply with growing demand through conservation, infrastructure investment, and allocation choices.
Arizona’s Primary Water Sources
Arizona relies on a diverse water portfolio that draws from three major categories of supply. The largest single source is groundwater, which accounts for approximately 41% of the state’s total water use, pumped from underground aquifers. However, much of this groundwater is non-renewable, meaning it is withdrawn faster than it can naturally recharge.
The Colorado River represents the state’s largest renewable surface water supply, providing about 36% of Arizona’s annual water. This water is delivered primarily through the 336-mile Central Arizona Project (CAP) canal, which brings water to the state’s most populous counties: Maricopa, Pinal, and Pima. In-state rivers, such as the Salt and Verde systems managed by the Salt River Project, contribute another 18% of the supply and are subject to their own separate, earlier water rights.
The remaining portion of the state’s water, about 5%, comes from reclaimed water, also known as effluent, which is wastewater treated and reused for purposes like agriculture, power generation, and environmental restoration. This diversity in sourcing provides a degree of resilience, as not all supplies are affected equally by the same drought conditions.
Current Supply Crisis and Shortages
The primary threat to Arizona’s water security stems from the historic decline of the Colorado River system, driven by a two-decade megadrought and increased aridification. Water levels in the system’s two main reservoirs, Lake Mead and Lake Powell, have dropped to historic lows, triggering mandatory cutbacks for the Lower Basin states. Lake Mead’s water level determines the severity of the shortage declaration, with specific elevations corresponding to different shortage tiers. A Tier 1 shortage is declared when Lake Mead’s level falls below 1,075 feet above sea level, initiating the first round of reductions.
The most recent shortage declaration requires Arizona to reduce its Colorado River water usage by 512,000 acre-feet, which constitutes approximately 18% of the state’s Colorado River supply. This reduction disproportionately impacts users who receive water through the Central Arizona Project, as nearly all of the federal cuts are borne by CAP contracts. These mandatory cuts are part of a framework designed to protect the reservoir system from falling to “dead pool” levels, where water can no longer flow past the dam.
The cuts fall most heavily on agricultural users in Pinal County, who hold the lowest priority water rights within the CAP system. This approach protects water for municipal users and tribes with higher-priority rights, demonstrating the immediate impact of the state’s complex allocation system.
Water Management and Allocation Priorities
Arizona’s water distribution is governed by a long-standing legal principle known as “prior appropriation,” often summarized as “first in time, first in right.” This system grants a superior, or “senior,” right to the person or entity that first put a water source to beneficial use. In times of shortage, users with junior rights must cease water diversions before those with senior rights are impacted.
The state’s reliance on the Central Arizona Project places it in a junior position relative to California for Colorado River water, a condition agreed upon during the project’s authorization. Within Arizona’s CAP supply, the priority system is stratified, with agricultural users often holding the most junior rights, specifically the Non-Indian Agricultural (NIA) pool. Consequently, these agricultural contracts absorb the initial, deepest cuts mandated by federal shortage declarations.
Municipal and industrial water users, including major cities like Phoenix and Tucson, generally hold higher-priority CAP contracts or rely on in-state river water with senior rights. This legal framework provides a significant buffer for urban areas, shielding most household and business water supplies from immediate federal cutbacks.
Strategies for Long-Term Water Security
Arizona is actively investing in long-term strategies to enhance water security and reduce reliance on the Colorado River. The 1980 Groundwater Management Act established Active Management Areas (AMAs) in the state’s most populated regions to regulate groundwater use. The goal in many AMAs is to achieve “safe-yield,” where groundwater withdrawals do not exceed natural and artificial recharge over time. The state also uses the CAP system to recharge aquifers, storing renewable water underground as a hedge against future drought.
Water reuse, or reclamation, is a growing component of the state’s future water portfolio, with investments aimed at maximizing the use of treated wastewater. Reclaimed water is already used for non-potable purposes, but advanced treatment could expand its use significantly, potentially recovering up to 30% of the water delivered by a potable system.
Infrastructure investment is another area of focus, including research into desalination, or removing salt from brackish groundwater or seawater. Importing desalinated ocean water from the Pacific or the Sea of Cortez is complex and costly, but the state is evaluating binational projects with Mexico to secure a new, drought-proof water source. These efforts signal a shift toward greater resource diversification and self-sufficiency.