In the face of a looming water crisis in the 1960s, Arizona embarked on an ambitious and transformative infrastructure project, the Central Arizona Project (CAP), to divert Colorado River water to its major cities and farmlands. Constructed over two decades, the 336-mile canal system supports the state’s two largest metro areas, Phoenix and Tucson. According to a recent AZPM feature, this massive endeavor has played a crucial role in shaping Arizona's growth.

As outlined in an interview with Zac Ziegler of AZPM's podcast "Tapped," the Mark Wilmer Pumping Plant is where much of Arizona's Colorado River water begins its journey through the CAP. Capable of filling an Olympic-sized swimming pool in under 30 seconds, the facility's pumps elevate water over the Buckskin Mountains to supply agriculture and urban areas with vital resources. Christopher Conover, also of "Tapped," pointed out that the bill authorizing the CAP was signed by President Lyndon Johnson in 1968, with actual construction commencing in 1973.

Such an intricate infrastructure doesn't come without its challenges or costs. The CAP was a federally funded project with an initial cost of $4 billion, in 1973 dollars, and Arizona is tasked with repaying approximately $1.6 billion of that investment. Rich Weissinger, director of field maintenance for CAP, underscored the sheer volume of water managed by the system, citing the canal's capacity of about 3,000 cubic feet per second, sustaining today below a million acre-feet of water annually.

The sustainability of Arizona's water resources required forward-thinking and sometimes complex legal and management strategies. According to Bruce Babbitt, the former governor who oversaw much of the CAP's construction, addressing the state's aquifer overdrafting was a crisis "fraught with possibility." A Department of Water Resources was created, a groundbreaking groundwater code was written, and water rights were quantified. This comprehensive approach has yet to be replicated elsewhere in the country, Babbitt told AZPM in an oral history.

Despite its significance to Arizona's development and consistency in supply, the CAP's delivered water represents untreated, raw river water. This means entities that utilize this water must have their treatment plants prepared for the incoming quality. Additionally, the CAP supports a diverse ecosystem within its channels, stocking certain types of fish such as grass carp and catfish to control algae growth and other potentially disruptive organisms, as mentioned by Weissinger.

Ultimately, the CAP's impact on Arizona's economy and landscape is undeniable. A 2019 report from Arizona State University, as highlighted by AZPM, found that the CAP contributed an estimated $2 trillion to the state's Gross Domestic Product over nearly 50 years. With agriculture once consuming the lion's share of CAP water, it has shifted, with municipal, tribal, and industrial uses now comprising roughly three-quarters of its deliveries. This transition reflects the evolving priorities and needs of a state that has been a significant player in the arid American Southwest.