Colorado River Shortage

is in decline.

• The river is "over-allocated," meaning that the total volume of water users are entitled to on paper each year nearly always exceeds the physical amount of water the system produces.
• Over two decades of drought have compounded the problem.
• Many experts believe that climate change will cause long-term reductions in the Colorado River's flows.

According to the U.S. Geological Survey, every temperature increase of 1 degree Celsius (1.8 degrees Fahrenheit) in the Upper Basin results in a 9.3% reduction in flows.

Today, this river system supplies water for 40 million people in seven western states and Mexico and irrigates more than 5 million acres of farmland.

Agriculture accounts for around 59% of total Colorado River water use and 74% of the Colorado River water consumed for human purposes; alfalfa and hay are the dominant crops.

There is much consternation about population growth in the Basin, but municipal uses are modest, and lower even than environmental ones. This is because, per acre,  urban water uses are typically much lower  than that of thirsty crops and riparian vegetation.

Agricultural, environmental, industrial, municipal, and tribal water users in seven states and the Republic of Mexico share the Colorado River via interstate compacts, Supreme Court decrees, and international treaties.

The Colorado Basin states, Mexico, the U.S. government, and numerous tribes, cities, and irrigation districts have entered into various agreements to try to prevent water levels in Lakes Powell and Mead from falling to critical levels.

In 2019 and again in 2023, agreements were reached to keep water in Lake Mead. These voluntary contributions are in addition to involuntary cuts mandated in the 2007 operating guidelines. Under certain reservoir conditions, some of the voluntary contributions can be "recovered" or delivered back to the entity that contributed the water.

Under these agreements, Arizona, California, Nevada and Mexico make increasingly large, voluntary contributions should Lake Mead’s levels continue to fall. Water users are also compensated to leave water in Lake Mead that cannot subsequently be recovered; this activity is called System Conservation.

The first-ever shortage was declared on the Colorado River in 2022. This was a Tier 1 shortage; Arizona was subject to an involuntary cut of 320,000 acre-feet and also made a voluntary contribution of 192,000 acre-feet to Lake Mead. Water levels continued to decline, and in 2023 Arizona was subject to an involuntary cut of 400,000 acre-feet and also made a voluntary contribution of 192,000 acre-feet to Lake Mead under Tier 2a shortage conditions.

The actions taken to shore up reservoir levels alongside record-breaking snowpack in the winter of 2022-23 improved water levels at Lakes Powell and Mead. Arizona went back into Tier 1 shortage in 2024 and remained there in 2025. However, the Colorado River system remains significantly over-allocated.

Because Colorado River water users in Central Arizona have lower priority rights than water users in Western Arizona and California, they take the largest cuts when a shortage is declared. 

The 2025 Tier 1 cuts, voluntary contributions, and System Conservation left in Lake Mead total around 30% of Arizona's Colorado River water and more than 50% of the water typically delivered through the CAP canal in non-shortage years.

That’s a lot of water, especially considering Arizona relies on the Colorado River for a little more than one-third (36%) of its water supplies. Other Arizona water supplies come from groundwater (41%), in-state rivers (18%), and reclaimed water (5%).

What does all of this mean for Arizona? And what comes next?

Follow along as we explain what the Colorado River shortage means for tribes, cities & private water companies, agriculture, water conservation, residential water users, groundwater pumping, an individual’s pocketbook, urban growth, new water supplies, water rights, and the future.

In Western Arizona, where water users have higher-priority rights and are relatively insulated from shortages, nearly all Colorado River water is used to grow crops. The Kyl Center has developed a  tool  that shows shortage impacts in Western Arizona under different hydrologic scenarios. Under most scenarios, most entitlement holders in Western Arizona experience relatively little impact to their water availability.

The story is very different in Central Arizona. To understand the impact of shortages in Central Arizona, it is first important to understand how mainstem Colorado River water is used there.

Tap Water

Tribes, cities, private water companies, mines, and power companies hold entitlements to Colorado River water in Central Arizona and they use the water in different ways.  A few municipal water providers take delivery of their Colorado River water at surface water treatment plants, where the water is treated to drinking water standards and distributed as tap water to customers; tap water uses in Central Arizona typically total a little more than 300,000 acre-feet per year. The Kyl Center developed a detailed  explainer  on the impacts of Colorado River shortage for tap water deliveries.

Agriculture

More commonly, tribes, municipal water providers, and mines deliver their Colorado River water to farmers.  The farmer uses the Colorado River water instead of groundwater to irrigate crops, and the groundwater thus “saved” becomes a water “credit”—a right to pump groundwater that can be used in the future, traded, or even sold.  These credits are valuable and there is an active market for them—they are called Long-term Storage Credits.  The Kyl Center has developed a  tool  where users can see how many long-term storage credits have been created in Arizona, and who owns them.

Apart from delivering Colorado River water to farmers to create Long-term Storage Credits, the Ak-Chin and Gila River Indian Communities and the Tohono O'Odham Nation also deliver Colorado River water for crops within their lands. Altogether, agricultural uses are estimated to total around 215,000 acre-feet in 2024, down from historic highs of over one million acre-feet.

The amount of Colorado River water used for agriculture in Central Arizona has declined over time for many reasons, including urban development on farmland, inability of irrigation districts to afford to pay for Colorado River water, involuntary cuts imposed in shortage conditions, pledged voluntary contributions to Lake Mead, and other reasons. More recently, tribes and municipal water providers have chosen to leave water in Lake Mead as System Conservation rather than deliver it to farmers to earn Long-term Storage Credits.

Aquifer Recharge

Cities, tribes, mines, and private water companies also use a large amount of Colorado River water for aquifer recharge in Central Arizona. Their water is delivered to specially-designed facilities that allow the water to percolate into local aquifers to replenish groundwater pumping and to create a bank of water that can be used in the future. In 2024, aquifer recharge is estimated to total nearly 240,000 acre-feet. 

Turf & Industry

The remainder of the Colorado River water estimated for delivery into Central Arizona in 2024, a small amount, will be traded for Salt & Verde River water, delivered directly to golf courses, or used directly in industrial processes.  Golf courses in the desert are the subject of much attention, but they use a relatively small amount of Colorado River water.  The majority of their water use is actually groundwater.

Here is a breakdown of how cities and private water companies in Central Arizona use Colorado River water:

It is also necessary to understand the water priority system in Central Arizona to understand the impact of shortages.

Most cities and private water companies in Central Arizona use groundwater to meet customer demands at the tap.  Colorado River water is then used to replenish the groundwater through aquifer recharge.  Examples include the cities of Tucson, Surprise, and Queen Creek, as well as Arizona Water Company.  For these municipal water providers, shortage on the Colorado River will impact their ability to recharge aquifers, but it will not impact their ability to deliver tap water.  That is, the impact of Colorado River shortage will likely play out over the long-term in the form of increased aquifer depletion, but will not create a short-term crisis.

The only municipal water providers that deliver Colorado River water as tap water are in the Valley of the Sun.  Examples include the cities of Phoenix, Scottsdale, and Mesa, as well as EPCOR Water Company.  Colorado River shortages may force these municipal water providers to change their operations and use alternative water supplies to deliver tap water. 

To see how individual municipal water providers' access to Colorado River water in Central Arizona will be impacted by increasingly severe cuts, explore the  Central Arizona Colorado River Shortage Impact Analysis Tool .

Alternative water supplies in the Phoenix-Mesa metropolitan area include groundwater, Salt & Verde River water, Agua Fria River water and reclaimed water. It is a bit trickier to use alternative supplies to meet customer needs at the tap because the placement and size of transmission mains and pipelines depend on the water supply source. Changing the water source may necessitate changes in infrastructure and operations.  As an example, the city of Phoenix invested hundreds of millions of dollars in new transmission mains and pump stations to develop the ability to move Salt & Verde River supplies into portions of north Phoenix that were historically dependent on Colorado River water.

Here is a breakdown of the types of water supplies that are used to meet demands for tap water among municipal water providers in Central Arizona that have entitlements to Colorado River water:

Water managers in Central Arizona are collaborative and innovative.  There will be opportunities to trade, lease, and sell water supplies.  For example, a city that needs Colorado River water at a surface water treatment plant can trade some of its Long-term Storage Credits with another city that uses its Colorado River water for aquifer recharge.  The first city will receive necessary deliveries at its water treatment plant, and the second city will receive the same amount of Long-term Storage Credits through trade that it would have received had it used its Colorado River water for aquifer recharge.

In Central Arizona only the Ak Chin Indian Community uses Colorado River water for tap water.  However, the Ak Chin Indian Community also enjoys the highest priority Colorado River water rights in Central Arizona; their tap water needs are not likely to be affected by shortage.

Most tribes deliver groundwater for tap water, and as for many cities and private water companies, their tap water deliveries will not be impacted by shortage.  Some tribes lease their Colorado River water to cities, private water companies, mines, and others.  The impact of shortage on these water supplies will be felt by the lessee, not the tribe.  Still other tribes deliver their Colorado River water to farmers to create Long-term Storage Credits, to aquifer recharge facilities, and to their own agricultural fields.  Many are compensated to leave water in Lake Mead as System Conservation. Under shortage conditions, tribes will have less water for these purposes. 

To see how tribal access to Colorado River water in Central Arizona will be impacted by increasingly severe cuts, explore the  Central Arizona Colorado River Shortage Impact Analysis Tool .

Farmers in Central Arizona can expect to continue to receive Colorado River water even under relatively deep shortage conditions because so many tribes, cities, private water companies, and mines deliver water to them for the creation of Long-term Storage Credits. The amount farmers receive under future shortage conditions will depend on many factors, including whether these entities will prefer to send their remaining Colorado River water to aquifer recharge facilities instead of irrigation districts, whether these entities will accept compensation to leave water in Lake Mead as System Conservation, and whether these entities enter into exchanges to help ensure that cities continue to receive enough Colorado River water to meet tap water needs.  

Northern Arizona

The city of Page operates a surface water treatment plant that relies on Lake Powell, and the city delivers drinking water to the LeChee Chapter of the Navajo Nation through an interconnection between each community's water pipeline network. The city and the Bureau of Reclamation have developed infrastructure that helps ensure that reliable water deliveries in Page and LeChee can continue even if Lake Powell water levels fall to the river outlet tubes, and are evaluating the development of a separate inlet station that would ensure these deliveries no matter how low water levels in Lake Powell fall.

There are no other plants that treat Colorado River water for drinking water in Northern Arizona. Nearly all communities in the area, including on the Navajo Nation and on Hualapai and Havasupai lands, rely on wells for drinking water supplies.

What does the Colorado River shortage mean for...

Should urban water users step up their water conservation efforts?

Yes, it would help — but urban users will never be able to conserve enough water to substantially offset the water losses created by shortage.

Although municipal users account for only a relatively small amount of the Colorado River water used in Arizona, long-term reductions in their water use is helpful because those reductions enable water providers to stretch available supplies to serve more people and businesses. Because over 90% of water used indoors is reclaimed and reused, reductions in water used for outdoor landscaping provide the biggest benefits.

While helpful, especially at a local level, reductions in municipal water use won’t necessarily translate into water left in Lake Mead.

Lower priority or junior priority users are entitled and eager to use water that more senior contract holders leave in the system.

What does the Colorado River shortage mean for...

Most Arizonans' primary relationship to water is when it comes out the tap in their kitchen or rains down on them from their shower. It's only natural that most Arizonans' primary question about the Colorado River shortage is how it will affect them, personally, as residential water users.

Will the Colorado River shortage impact me?

Probably not in the next few years because the impacts mainly mean that less water is available for:

• aquifer recharge and replenishment, and
• farmers in Central Arizona, who gave up their long-term contracts for Colorado River water decades ago in exchange for subsidized water that is first to be cut during a shortage
  • Farmers have turned to groundwater as a replacement source.

But in the next few years...

• The cost of water delivered through the Central Arizona Project will increase, and if you live in Central Arizona your water bill may rise.
• Water providers plan proactively to ensure reliable water deliveries even in shortage. Many water utilities have access to alternative supplies — groundwater, reclaimed water, and Salt and Verde river water, for example — but alternative supplies and the infrastructure necessary to deliver them may be more expensive, and increased costs will be passed on to customers.
• Your property tax bill may increase if you live in a subdivision that is a member of the  Central Arizona Groundwater Replenishment District (CAGRD)  because the district partially relies on Colorado River water to replenish groundwater pumped for its members and may need to acquire more expensive replenishment supplies.
• If you are in a CAGRD Member Service Area (rather than a CAGRD Subdivision), you may also see an increase in your water bill due to higher costs of replenishment water. Not all member service areas incur replenishment fees. 
• There will be less water available to artificially recharge Central Arizona aquifers, which will exacerbate groundwater depletion.

The Kyl Center for Water Policy examines the role of the CAGRD in a special report,  "The Elusive Concept of an Assured Water Supply: The Role of CAGRD and Replenishment." 

Use the map below, which is derived from the  Arizona Water Blueprint , to determine whether you live in a CAGRD Member Land Subdivision.

Click and drag to move around the map or use the Search feature in the top left corner to find an address or place.

What does the Colorado River shortage mean for...

Check out the Kyl Center's report on  groundwater use in the Valley of the Sun 

• Arizona has stored a large amount of Colorado River water in aquifers in Central Arizona in preparation for shortage.
• However, groundwater pumping will increase as farmers, cities, and private water companies in Central Arizona receive less Colorado River water.
• Increased groundwater pumping reduces the availability of this finite water supply for future needs, including municipal and industrial uses.
• While groundwater use in the three Central Arizona counties that receive Colorado River water has decreased since 1980, groundwater is still being pumped at unsustainable levels.
• Overpumping of groundwater supplies has well-documented consequences, including land subsidence, water quality degradation and increased costs.

Explore how groundwater levels in Arizona have changed over time using the Kyl Center's Groundwater Level Application.

What does the Colorado River shortage mean for...

The cost of water will very likely increase.

• Your water bill comes from your local water utility. Most water utility costs are related to infrastructure — water mains, pumps, tanks, treatment plants, and meters, for example — but the cost of wholesale water supplies is also significant.
• Colorado River water is delivered on a wholesale basis to some, but not all, water utilities in Central Arizona. The cost of these deliveries is passed on to customers.
•  The cost of wholesale Colorado River water delivered through the Central Arizona Project will increase due to shortages. 
• Different water utilities depend on wholesale supplies from the Central Arizona Project to varying degrees. Those that are more dependent will experience cost increases that are relatively higher.
• Many water utilities have access to alternative supplies — groundwater, reclaimed water, and Salt and Verde River water, for example — but alternative supplies and the infrastructure necessary to deliver them may be more expensive, and increased costs will be passed on to customers.
• Costs for water for replenishment will likely rise, either directly through a rate increase or indirectly through property taxes. 

Use the map below, which is derived from the  Arizona Water Blueprint , to learn more about water providers in your area. Pop-ups provide links to annual reports, plans, and more information from the Arizona Department of Water Resources.

What does the Colorado River shortage mean for...

A shortage declaration has been anticipated for many years, so the shortage will not come as a surprise to Arizonans involved in planning for water for growth.

Central Arizona still has some water for growth.

Two important things to keep in mind...

• Population growth and water demand have become “decoupled” as municipal water users have become increasingly efficient in their water use. In the last two decades, the municipal population of CAP’s three-county service area has grown 45% but municipal water demand has increased only by 14%.

• In Central Arizona, municipal water planning occurs on long timelines, and for many years plans for urban growth have not counted on the Colorado River supplies at high risk of being cut.

Remember, the shortage will primarily impact water users in the CAP service territory, which covers most of Maricopa, Pinal, and Pima counties.

The supplies of Colorado River water for users in Western Arizona will not be cut.

Some Central Arizona communities will not be significantly impacted because they have sufficient water supplies to support their projected growth and have factored potential Colorado River reductions into their long-term water resource plans.

But even in these communities, reduced Colorado River supplies may mean water rates must increase to pay for the infrastructure needed to deliver alternative supplies and to cover the higher costs of the water supplies available.

Some Central Arizona communities are actively reckoning with how to ensure water for growth, and the prospect of long-term declines in Colorado River supplies has helped focus their attention on finding new water supplies and new ways to stretch available supplies to meet greater demand.

What does the Colorado River shortage mean for...

Many communities in Central Arizona have sufficient, reliable renewable water supplies to meet their future demand. 

But some communities don’t have all the water they need for their projected growth, and Colorado River shortage has increased interest in augmentation projects — that is, projects to bring new water supplies into Central Arizona. The Arizona Legislature has set aside hundreds of millions of dollars to help fund future augmentation projects.

Three things to think about with respect to new water supply projects...

1. The water users most immediately impacted by the Colorado River shortage — Pinal County farmers — are unlikely to benefit from a water augmentation project. Why? Because any new supplies of water will be too expensive to be used to grow crops.
2. Typically, the communities that benefit from new water supplies are the ones who must pay for that water and the infrastructure to treat and deliver it. For a water supply project to be financed, the lender must have some assurance that the borrowers have the capacity to pay back the loan. Proving that there will be enough future demand to pay off that financing can be challenging.
3. Investments in efficiency, conservation and re-use are in many instances less expensive, gallon-for-gallon, than investments in new water supplies.

The Kyl Center for Water Policy developed the application below to explore the proposals and projects that aim to augment water supplies in Arizona.

Learn more about how water infrastructure projects are funded from the Water Infrastructure Finance Authority of Arizona.

What does the Colorado River shortage mean for...

In the American West, the use of water is controlled by long-standing rights that can’t be altered just because water is scarce.

This water rights system has given cities, towns, industries and tribes the needed certainty to invest in the infrastructure necessary to treat and deliver water and helps to ensure reliability in times of shortages.

While some would like to “take” water from existing uses and give it to a different use, that’s unlikely to happen.

Here’s why:

The use of Colorado River water is governed by a complex set of agreements, court decrees and federal laws, collectively known as the Law of the River. Most rights and contracts to use Colorado River water are “in perpetuity,” meaning they last forever.

Colorado River water delivered through the CAP is regulated by a master agreement between the U.S. Secretary of the Interior and the Central Arizona Water Conservation District, a state-created entity that operates the CAP and is responsible for repayment of CAP construction costs to the federal government.

In 1983, the Interior Secretary allocated Colorado River water delivered by the CAP to municipal and industrial water users, Indian tribes and agricultural entities in Central Arizona, which then signed individual contracts with the Central Arizona Water Conservation District and the Interior Secretary for delivery of this water.

 While agricultural entities in Central Arizona subsequently gave up their contracts, municipal and industrial users and Indian tribes retain permanent contracts. 

The ability to use water from Arizona’s in-state streams, such as the Salt River, is similarly regulated under court decrees or state-granted water rights. Arizona follows the doctrine of prior appropriation, often referred to as “first in time, first in right.”

This means that the first person to use or divert water from a river or stream for a beneficial purpose has a right to that water over any subsequent users. As a result, in times of shortage, later users are more likely to have their access to water cut.

Water rights — whether granted pursuant to a contract, a court decree or a permit from the state — are vested rights, which generally cannot be taken away or diminished without consent of the owner.

However, water managers in Arizona have created innovative, voluntary leases and exchanges that allow them to move water to preferred purposes to create additional value and resiliency, all while respecting our existing water rights structure.

The current guidelines for the long-term management of the Colorado River system will expire at the end of 2026. Before then, the U.S. Department of Interior will work with the Basin States and tribes through a reconsultation process to develop a new set of operating guidelines for how to deal with dry years and declining supplies.  

 The Kyl Center for Water Policy,  along with Arizona State University’s  Decision Theater,  is developing a shortage impacts model and advanced visualizations to enable more people to understand and participate in developing solutions to the state and region’s water challenges.

 Our effort is called the Arizona Colorado River Visualization Enterprise (Arizona CuRVE). 

Stay tuned!