Understanding Arizona’s Water Position
Regional leaders have prioritized water management in the arid environment of Arizona since before it was recognized as a state. From canal and dam construction in the late 1800s and early 1900s, Colorado River treaties and compacts with neighboring states and Mexico preempting the Colorado River Basin Project Act in 1968 to the 1980 Groundwater Management Act, Arizona’s growth in the 20th century was centered around intentional, proactive water management.
Today, even with the massive population growth and advanced industries expanding into Greater Phoenix, Arizona water usage has decreased from 1957 due to intentional conservation, advancements in reclamation and an economic shift away from water-heavy agriculture. The state has several different regulated water sources, the vast majority of which are reclaimed or renewable. The Colorado River shortage declaration necessitated by the 20-year drought is expected to impact Arizona less than its southwest neighbors because of the dedicated planning over the last century.
of water that is flushed or goes down the drain is reclaimed
acre-feet of water is stored in AZ reservoirs & underground
AZ communities within an AMA must assure a 100-year water supply before platting new development
What are Arizona’s water sources?
Arizona has four main sources of water:
- Colorado River water
- In-state surface water
- Reclaimed water
Most groundwater used in state is fossil groundwater. In-state surface water, reclaimed water and Colorado River water are all renewable, with rivers such as the Salt and Verde replenished by annual precipitation.
Arizona relies less on the Colorado River than neighboring regions do. A little more than one-third of the state’s total water use is from the river, while southern Nevada (90%), southern California (60%) and Colorado (40%) rely more heavily.
The Tier 2a Colorado River shortage primarily falls on the Arizona Water Banking Authority which uses water to recharge aquifers, and farms, particularly irrigation districts in Pinal County.
A large amount of water from the river has been banked in local aquifers and can be used during shortages.
The majority of Arizona’s surface water comes from Salt River and Verde River, both managed by the Salt River Project. These watersheds are less susceptible to climate change than the Colorado River is, providing a more reliable source. The annual water demand in this system has declined over the last few decades.
SRP water is available to many cities in Greater Phoenix. About 40% of tap water comes from the Salt and Verde rivers, while groundwater provides 26% and the Colorado River makes up 34%.
SRP’s reservoirs are at full capacity as of April 2023. Arizona has 12 million acre-feet of water in reservoirs and underground — 1.75 times more water stored than it uses.
The 1980 Groundwater Management Act, which pushed urban growth to renewable surface water supplies, established the legal and physical infrastructure to assure a 100-year water supply in active management areas (AMAs) before development can be platted.
Groundwater is primarily regulated under two designations: Irrigation Non-Expansion Areas (INAs), which regulates wells, & AMAs, which regulates high-groundwater reliant zones. Five areas with heavy reliance on mined groundwater were identified and designated as AMAs to help meter, regulate and report on groundwater use. The Phoenix AMA has a management plan updated every 10 years to address water use by all sectors.
Arizona Water Management
Arizona’s total annual water demand is around 7 million acre-feet, and each municipality, community or water provider has its own portfolio of supplies to manage the demand.
Almost all water that enters urban wastewater treatment systems can be reclaimed and reused. Ninety-three percent of water that goes down a drain, including that which is flushed, is reclaimed, and only 17% of agricultural flood irrigation results in incidental aquifer recharge.
The 1980 Groundwater Management Act regulates the use of groundwater, specifically though INAs and AMAs.
- In INAs, wells larger than small residential wells are metered. Groundwater usage is required to be reported annually.
- AMAs require metering and reporting of groundwater use, prohibit new irrigated agriculture, and require proof of a 100-year water supply that is physically, financially and legally available before a development of six or more homes can be platted.
Every 10 years, ADWR develops a new management plan for each AMA.
Advancing toward safe yield
The management goal for the Greater Phoenix AMA is to achieve safe yield, the long-term balance between the amount of groundwater withdrawn and replenished.
There are seven groundwater basins within the Greater Phoenix AMA. Over the last 10 years, groundwater levels have increased in the Carefree Basin and the East Salt River Sub-basin but decreased in the Rainbow Valley sub-basin. The other four sub-basins have been stable. Despite this, the Arizona Department of Water Resources (ADWR) in 2020 quantified unreplenished groundwater demand in all AMAs in the state. While conservation is necessary, that alone will not lead to safe yield.
Colorado River shortage
The Tier 2a Colorado River shortage was declared in 2023, prompting a cut of 592,000 square feet of water primarily on the Arizona Water Banking Authority and the irrigation districts in Pinal County. While Greater Phoenix does not rely on the Colorado River as much as other regions in the basin, water portfolios must be adjusted to offset losses from the river.
Municipalities will use groundwater and other supplies to backfill the shortage, while promoting conservation programs to reduce outdoor water use and commercial cooling water use.
Communities will look at alternative supplies such as the transfer of agricultural water rights to urban areas, additional leases of water held by Native American communities, direct potable use of reclaimed water, recovery of Colorado River water that was previously banked underground, desalination of brackish groundwater, and water available through expansion of the capacity of local reservoirs.
The state budget has set aside money to advance water research and increase water treatment efficiency.
Looking to the future
A U.S. Bureau of Reclamation study projected a West Valley water shortage by 2060. No model was publicly available for the rest of the region. Over the next 35 years, Greater Phoenix will look to different avenues to rectify this challenge.
The Water Infrastructure Finance Authority (WIFA) will be a key driver in future planning for the long-term water supply. Its budget allocation includes:
- $1 billion for projects that import new water supplies
- $200 million for financing improvements in municipal water infrastructure
- $200 million in water conservation grant funding
While desalination is a long-term goal, delivery at scale is currently cost prohibitive. In addition to desalination, future water resources could include brackish groundwater, direct potable reuse of reclaimed water, transfers of Colorado River water rights or limited inter-basin transfers of groundwater.
The Inflation Reduction Act (IRA) includes $4 billion that will go toward water management and conservation efforts in the Colorado River Basin.