In the desert, perhaps more than anywhere, water is the source of a flood of questions:

-�Do we have ample supply for Arizona's needs today and tomorrow?

-�Are we in a current water crisis? And, if so, what's being done and what

should be done?

-�Why do we keep encouraging growth if our water future is in doubt?

-�Will a growing population's thirst prompt more people to move to water-rich

areas, causing other areas to, metaphorically and literally, dry up?

-�Do we need to alter how we live by doing things like banning swimming pools?

These questions and more are considered in a new report, "Watering the Sun Corridor: Managing Choices in Arizona's Megapolitan Area," produced by Morrison Institute for Public Policy.

The report was written, in part, to address a string of recent pronouncements that urban Arizona is "unsustainable" or "running dry" or at "extreme risk" from climate change because the gap between precipitation and water use is great and likely to increase.

As chief author of the report, I should first explain the word "megapolitan." It was taken from our 2008 report, "Megapolitan: Arizona's Sun Corridor," which refers to the growing Phoenix-Tucson area, which forms the heart of urban Arizona.

The new report includes lower estimates for growth in the Sun Corridor but still projects a population increase from 6 million today up to 10 million by 2040.

So, is there enough water? Complex question.

The very definition of water supply is a fluid matter, depending on priorities and jurisdictions, method of measurement, shifting needs (agriculture to urban, for instance), differing experts interpreting the same data and, yes, even climate change.

The dynamics of these variables are discussed in "Watering the Sun Corridor." Weighing in are Ray Quay and Patricia Gober of Arizona State University's Decision Center for a Desert City; Sharon B. Megdal of the Water Resource Research Center at the University of Arizona; and Pinal County Supervisor David Snider.

The report will be available at MorrisonInstitute.asu.edu on Thursday on the Web.

"Watering the Sun Corridor" offers more details than I can provide in this limited space. But here are a few highlights:

-�Because water supply in a desert is highly variable, the Sun Corridor has built a watering system with multiple inputs and storage capacity far in excess of many other places.

-�Even accounting for current projections of the impact of climate change, the Sun Corridor's watering systems can likely support about 9.5 million people at current rates of consumption - but to do that will require virtually eliminating commercial agriculture.

-�We have done a good job of reducing per capita consumption and reusing effluent, but to continue population growth will require hard choices, primarily about landscaping and lifestyle.

-�The complexities of water rights and delivery systems will influence where and how growth occurs.

The Sun Corridor is not going to dry up any time soon, and most of the apocalyptic reports about the impact of climate change and drought on the desert Southwest have ignored the complex infrastructure and legal systems supporting our water supply.

But the challenges of an arid environment and an ever more variable climate are very real. In the past, those challenges were met with dams, wells, canals and recharge basins, not to mention court decrees, legislation, treaties and compacts.

All in all, it is a pretty remarkable story of human ingenuity. Water, among all things, has been what Arizona does really well.

In fact, the watering systems of the Sun Corridor stand as a shining example of the collective will of previous generations of Arizonans to build civilization in a harsh and difficult environment.

Will we have enough water for the next few generations - and generations beyond that?

Tomorrow's answer lies in today's question of whether we still have a shared commitment to this place and its future and whether we still trust in the power of collective action to meet new challenges with the same faith and creativity as yesterday.

Grady Gammage Jr., an attorney, author and land-water expert, is a senior research fellow at Morrison Institute for Public Policy, a nonpartisan center for research, analysis and public outreach at Arizona State University.