Water Bank: Arizona’s Emergency Savings Account

By Warren Tenney

In the early 1990s, Arizona was not using all the water it was legally due from the Colorado River. Instead, much of Arizona’s unused water flowed down the Colorado River to California. Here’s why: Under the law that governs the Colorado River, the Secretary of the U.S. Department of Interior can give water not used by one state to other states. As a result, each year California was the beneficiary of at least some of Arizona’s unused water. At the time, there were also concerns that Nevada would soon eye Arizona’s unused allotment.

Arizona’s Colorado River water is used in multiple ways. One major use is to irrigate agricultural lands along the Colorado River, most prominently in the Yuma region. In addition to on-River farming, more than half of Arizona’s allotment goes to municipal, tribal and agricultural users in Central Arizona. These users receive the water through a 336-mile canal that transports water across the state called the Central Arizona Project (CAP).  Since most municipal, tribal and agricultural users did not use their full allotments of water in the 1990s, their unused Colorado River water went to California. This was an unsettling predicament for a desert state that expected a surge in population.  Arizona’s mantra became “leave no water on the River.”

To address concerns that Arizona’s water was going to California, water managers AWBA Logodeveloped a concept to deliver unused water through the Central Arizona Project to store underground. This stored water would act as a buffer for times of drought. With support from the Arizona Department of Water Resources, AMWUA, and others in the water community, the Arizona Legislature in 1996 established the Arizona Water Banking Authority, more commonly called the Water Bank. Today, the Water Bank has stored 3.4 million acre-feet of water for Arizona. (One acre-foot of water serves an average of three Arizona households for a year.)

Here are the two ways the Water Bank stores water:

1. Underground Storage Facilities: With help from CAP, the Water Bank delivers Colorado River water to one of many underground storage facilities in central and southern Arizona. CAP, cities and other water agencies operate these storage facilities. These water storage sites consist of large constructed ponds called recharge basins. These basins are designed to allow the water to easily percolate into the ground. The water enters the natural aquifer where it is available to be pumped up through wells and delivered to customers affected by a shortage of Colorado River water.

Southern Avra Valley Storage and Recovery Project. Courtesy of Tucson Water.

Southern Avra Valley Storage and Recovery Project. Photo: Tucson Water

2. Groundwater Savings Facilities: These facilities work as a water exchange. In this case, Colorado River water is delivered to participating agricultural lands and used to irrigate crops. Participating farms or irrigation districts that receive river water agree not to pump an equal amount of water from the aquifer, thereby “saving” water underground. In the event of a Colorado River shortage, the water that was saved in the aquifer would be pumped or “recovered” and delivered to customers, such as cities, to help make up for shortages.

In recent years, CAP has had less unused or “excess” water. This is because municipal, tribal and agricultural users have been using more and more of their CAP water allocations.  As a result the Water Bank has less unused water to store from the “excess pool.”  When there was more excess water, the Water Bank stored an average of 250,000 acre-feet of water a year. In the last two years, that number has dropped to an average of 65,000 acre-feet.

There is currently a 56 percent chance the Secretary of the U.S. Department of Interior will declare a shortage of Colorado River water as early as 2018. Under the law that governs the Colorado River, the Secretary declares shortages based on the water levels in Lake Mead, the giant reservoir that sits behind Hoover Dam on the Colorado River at the Arizona-Nevada border. A 16-year drought has driven Lake Mead to its lowest level since the dam was completed in 1936. A possible 2018 shortage declaration would not affect the water supplies for cities, but would impact agricultural users and the Colorado River “excess pool” from which the Water Bank draws its water.  

The Water Bank has allowed Arizona to take all of its water off of the River and store it for a “dry” day.  The 3.4 million acre-feet of water stored by the Water Bank is a key component of Arizona’s preparations for eventual shortage.  As part of these efforts, it is important that the Water Bank, CAP, and water users develop a comprehensive plan for how the stored water can be recovered to help cities if a shortage declaration impacts their water supplies. 

The creation and operation of the Arizona Water Banking Authority is just one more example of how Arizona has led the way in water investment and innovation. This legacy continues to drive the water community as we tackle the challenge of looming shortages on the Colorado River.

For 46 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.

Safe-yield: A Balancing Act For Arizona’s Aquifers

By Warren Tenney

The goal of safe-yield has motivated Arizona’s cities to maximize their use of renewable water supplies – such as river water or recycled wastewater – and to minimize pumping groundwater. Safe-yield means the amount of water pumped out of the ground is the same as what goes back into underground aquifers. The efforts of Arizona’s cities to use renewable supplies and to protect groundwater have helped the Phoenix metropolitan area to weather a 16-year drought.  It is also why we are able to sustain long-term economic strength and enjoy our desert lifestyle.  Arizona’s innovative groundwater law—known as the Groundwater Management Act of 1980—designated safe-yield as a goal for the Phoenix Metro area. 

Groundwater is rain and snowmelt that has settled over thousands of years between rocks and gravel beneath the surface of the Earth.  Groundwater that settles in aquifers is a finite source of water.  Before 1980, uncontrolled pumping was depleting central Arizona’s groundwater, resulting in a lower water table, fissures in the ground, and cracked building foundations.  The Groundwater Management Act required farmers and cities to stop the unsustainable pumping of groundwater and encouraged them to use more water from the Colorado, Salt and Verde Rivers. Today only about 7 to 10 percent of the water used by AMWUA cities is made up of groundwater.

To help meet the safe-yield goal of the Phoenix area, cities financed the construction of treatment plants and other infrastructure necessary to use river water and recycled wastewater. Cities also have invested in storing water underground to meet and sustain safe-yield.

How To Recharge An Aquifer

Storing water underground is known as “recharging” the aquifer. Cities recharge water for at least two purposes: (1) to build up a bank account of water underground for times of drought, and (2) to offset groundwater that a city pumps and delivers to businesses and citizens. There are several ways to recharge or store water in an aquifer. Here are a few.

  • Recharge Wells: Cities build two main types of wells to recharge water into an aquifer. The first is a well dug 150 to 200 feet into the ground to direct water back into the aquifer. These are called “vadose zone wells” because they are sunk through the vadose zone or the upper part of the aquifer. The second type of well is called an “aquifer storage and recovery well” or ASR. This is a deeper well that goes 600 to 1,000 feet into the middle of the aquifer. These wells allow cities to both pump water directly back into the aquifer and pull it back out when needed.


    A vadose zone well in Scottsdale.

  • Recharge Basins: Some cities create basins filled with recycled wastewater or river water. The basins are built to help the water easily percolate back into the ground. These are known as recharge basins. Recharge basins come in a variety of sizes, from large regional facilities that allow multiple entities to store water at one location, to smaller recharge basins often owned by individual cities. Some cities create recharge basins on the site of their treatment plants, while others turn portions of them into recreational areas. For example, the Town of Gilbert turned some of its recharge basins into a 110-acre wildlife habitat called the Riparian Preserve at Water Ranch, located near Guadalupe and Greenfield roads.
  • Managed Recharge: Some cities receive permits to discharge river water into normally dry streambeds, where the water filters back into the aquifer.

    "Aerial shots of GRUSP"

    Granite Reef Underground Storage Project is a regional storage facility. PHOTO: Salt River Project

How Cities Make It Happen

Like many Valley cities, the City of Scottsdale recharges water into its aquifers as part of its commitment to contribute to the region’s goal of safe-yield. The City recharges most of this water within the city limits through vadose and ASR wells, and it also recharges water at regional recharge basins owned by Salt River Project and the Central Arizona Project.

Along with water from the Salt and Verde Rivers delivered by SRP, Scottsdale receives water from the Colorado River through the Central Arizona Project (CAP). Each October, Scottsdale Water places an order for its annual allotment of 80,000 acre-feet of Colorado River water with Central Arizona Project. One acre-foot of water serves an average of three Arizona families for a year.  Scottsdale’s current demand for Colorado River water is about 60,000 acre-feet per year. This leaves 20,000 acre-feet available to store.

Scottsdale sends the remaining 20,000 acre-feet of Colorado River water to one of two regional recharge facilities in Maricopa County. These recharge facilities provide two advantages. First, the facilities allow the city to return the water to the aquifer, which allows Scottsdale to do its part towards the safe-yield goal for the Phoenix metro area. Second, it allows the city to store or bank additional water it doesn’t need immediately for future use.  

The state’s water agency, Arizona Department of Water Resources, tracks the amount of water each city pumps out and recharges back into the ground. The agency does this to monitor if a city is contributing to the regional goal of safe-yield. The Department also tracks the amount of water each city returns to the aquifer as storage and gives the city a “long-term storage credit” for each acre-foot it stores, minus a 5 percent donation to the aquifer. This will allow cities to withdraw the correct amount of water when it is needed. 

What It Means To You

In 1980, wells in Maricopa, Pinal and Pima counties pumped out 2.3 million acre-feet more groundwater than could be recharged naturally. In 2013, the groundwater overdraft in Maricopa, Pinal and Pima counties had been reduced to about 382,000 acre-feet due to the Groundwater Management Act, including efforts to reach safe-yield.

The Groundwater Management Act only applies to the state’s five most populated areas called Active Management Areas. In recent years, the Phoenix Active Management Area has met its safe-yield goal.  The challenge is to continue to sustain safe-yield and ensure we have water to meet our future demand.  AMWUA cities will continue to seek and promote solutions to ensure that central Arizona achieves safe-yield to protect our most valuable resource—water.

For 46 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.



















Salt River: Bringing Life To A Desert Valley

By Warren Tenney

A likely shortage of Colorado River water in Arizona is big news. It should be. Colorado River water makes up 44 percent of the state’s water supply delivered through 336-miles of canals and pumps known as the Central Arizona Project. Colorado River water is important to Arizona but it is not the state’s only source of drinking water.

Salt River Project (SRP) operates eight dams, seven reservoirs and 131 miles of canals that bring water from the Salt and Verde rivers to the Phoenix metropolitan area. SRP provides 12 percent of Arizona’s water and is the largest provider of water to the Phoenix Metropolitan area.

A Short History

The Salt River has served the Valley since the ancient Hohokam people settled here in the year 300 A.D. These Native Americans built a 500-mile canal system that brought river water into their villages and fields for the next 1,000 years. They vanished around 1450.

The Hohokam had been gone nearly 400 years when an 1860s gold rush attracted fortune seekers to the Salt River Valley. Among them was Jack Swilling, an ex-Confederate cavalryman, who saw an opportunity to use water from the Salt River via canals to grow crops. He sold those crops to miners and the U.S. Calvary stationed at Fort McDowell.

Individuals, private companies, and associations started digging dozens of ditches trying to replicate Swilling’s success. The luckiest of these ventures lasted 30 years. Then came the same natural phenomenon that historians suspect pushed the Hohokam from the Valley: drought. The Salt River could no longer provide enough water for all the canals and thousands of acres of crops withered. Like the Hohokam, hundreds of pioneers left the desert village. 


To thrive, Phoenix needed a dam that would collect and store river water in the mountains to the north and east. The 1902 National Reclamation Act provided Phoenix with federal loans to build two dams on the Salt River, Theodore Roosevelt and Granite Reef Diversion. The federal government also bought out the ditch companies and connected all the canals into one system.

Ranchers and farmers who had remained in the Salt River Valley organized the Salt River Water Users’ Association and pledged their lands as collateral for the federal loans. In 1917, the federal government turned over the operation of the canal system to the Salt River Valley Water Users’ Association, which continues to operate the canals for the federal government as the Salt River Project.

Roosevelt Dam provides both a reservoir and hydropower. The Roosevelt Dam began supplying hydroelectric power to a copper mine in 1912. To increase its power capacity, SRP built three more dams along the Salt River before 1930. By 1946, SRP had built two dams on the Verde River. (These dams do not generate hydropower.)

After World War II the Salt River Valley was rapidly turning into an urban center that needed water for residential customers, rather than solely ranchers and farmers. In 1952, the City of Phoenix established the first contract with SRP to divert water from its canals to treat and deliver to homes. By 1984, SRP was delivering 55 percent of its water to Valley cities.

How It Works

The Salt and Verde rivers flow into Roosevelt Lake behind Roosevelt Dam. The reservoir can hold 1.6 million acre-feet or enough to meet SRP contracts for two years.

Canyon Lake

Canyon Lake

  • The water then runs through three reservoirs that are popular recreation lakes for Valley residents: Apache, Canyon and Saguaro. The Verde River water flows through Horseshoe and Bartlett lakes.
  • The water is released back into the Salt and Verde rivers, which eventually converge behind the Granite Reef Diversion Dam east of Mesa.
  • From there the river water enters into the Valley’s familiar canal system via gravity and is distributed to city water treatment plants and to farms.

SRP serves water to a 375-square-mile area and electricity to more than 1 million customers. The total SRP system today is about 55 percent full – just about the same as one year ago. In this 16th year of drought, the January-to-May snowmelt into the Salt and Verde rivers was below the median flow for the sixth consecutive year. The bright spot? The Phoenix metropolitan area has reduced its demand for water over the last 20 years.

What It Means To You

The Salt River and the Colorado River provide the AMWUA cities with a robust water supply. SRP makes up 53 percent of the water portfolio for the 10 largest cities in Maricopa County.  Having more than one source of water means a stronger economy for the Valley and a more reliable source of water for you.

SRP is unique to Arizona. We are all stewards of the Salt and Verde rivers. The watershed and forests that created and nurture these water sources must be managed well. We all have a responsibility to protect our watershed and forests, whether through making certain our actions do not cause a fire when camping or getting involved in forest restoration efforts. The health of our forests impacts the quality and sustainability of our water. 

Want to learn more about Salt River Project? Here’s a great place to begin.

For 46 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.

Fourth of July: Celebrating Our Water History

By Warren Tenney

Independence Day. However you celebrate – whether by the pool or watching fireworks with your favorite drink in hand – it is an excellent opportunity to contemplate what we often take for granted, such as affordable, safe water. Today we have safe drinking water at a reasonable cost delivered right inside our homes and businesses.

During the first century of our history, getting water often involved hauling it short or long distances in all types of weather. By the mid-1800s many cities had built centralized water systems, though most Americans did not enjoy indoor plumbing. During this period, pipes for water systems were made out of wood.  Even though iron pipes began to be used in the early 1800s, wood continued to be the more prevalent piping material. In the early 1900s, 30 miles of redwood pipeline brought water to the Phoenix area from the Verde River. It was not until after 1927 that the redwood pipelines began to be replaced with concrete pipes.

4th of July graphic 

In addition to the challenges of distributing water, people who operated early American water systems knew little about contaminated water. This created health issues for people.  In the 1800s, American cities were frequently hit with outbreaks of disease, such as cholera and typhoid.  In the 1850s, a link was made between contaminated water and disease.  Water treatment plants were built that used slow sand filtration and public health improved.  In the early 1900s, treatment plants began using chlorination, which led to an even more dramatic drop in water-borne diseases.  Today, the AMWUA cities deliver high quality drinking water because they invest in state-of-the-art treatment plants and dedicated professional operators.  This remains quite the achievement when you consider that clean water is still a luxury in many parts of the world.  Today, Water for People reports that 1.8 billion people around the world lack access to safe water and 2.4 billion do not have adequate sanitation.  More than 840,000 people die each year from water-related diseases. 

Historically, even in the United States, the conveniences of safe water and indoor plumbing have been the exception rather than the rule. In the 1830s, citizens were amazed when hotels in Boston and New York began offering indoor communal bathrooms to guests. In 1871, Tucson could boast a population of 3,000, a newspaper, a brewery, two doctors, a number of saloons, and one bathtub.  Indoor plumbing did not become an expected feature in all American homes until well into the 20th century. 

The availability of water was key to the settling of the West.  In Arizona, the Salt River Project was able to move water from miles away to guarantee the settlements in the Phoenix area thrived.  With water from the Salt and Verde River system and the Colorado River, the AMWUA cities have put together strong water portfolios to make water available to the millions of us who live here.  It takes thousands of miles of pipe running underground to deliver water to our homes. Each AMWUA municipality – Avondale, Chandler, Gilbert, Glendale, Goodyear, Mesa, Peoria, Phoenix, Scottsdale and Tempe – has hundreds of dedicated water professionals who operate and maintain its water systems to ensure we have water whenever we need it.

We also enjoy this plentiful high-quality water at a reasonable cost.  In the late 1800s, burros would transport water from springs to the small number of residents in Tucson.  Vendors would sell the water for about five cents a gallon.  Today, clean water delivered to your home and work costs, on average, one-third of a penny per gallon.  And no burro has to deliver the thousands of gallons of water most residents use each month.    

So as you enjoy this Fourth of July with your family and friends, imagine how different your celebration would be if affordable, safe water did not flow from your indoor and outdoor faucets.  Give a shout out for the freedoms we enjoy in the United States.  And remember to add a cheer for the water we enjoy due to the hard work and effort of many individuals at your water utility, both past and present.

Tucson information is from The Book of Tucson Firsts by Larry Cox (1998). 

For 46 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.