The Arizona Republic's Shaun McKinnon did a fine job of using the breach in the CAP canal to provide a primer on the system and some of its challenges (here, here and here). This blog has written extensively on water and Arizona, but while a few people are paying attention, let me make a few essential points:
• The Colorado River is over-subscribed. There are, as the water geeks say, too many straws sucking from the river. When the Colorado River Compact was first sealed in 1922 (with Arizona disputing the allotments, chiefly because it believed it was due more because the Gila and its in-state tributaries flow into the Colorado), the Southwest was largely unpopulated and even Los Angeles' population in the most recent Census was less than 600,000. The river was to be "tamed" for reclamation. Nobody ever imagined Las Vegas, a tiny stop on the Union Pacific Railroad, would become a major metropolis. Critically, the river levels used to make the allotments were around 500-year highs. Now there's simply not enough water to go around. The Upper Basin states, especially the state of Colorado, always felt defrauded by the deal and the subsequent settlement of Arizona v. California. They will be much more jealous of their water resources now. Mexico was shortchanged, as well, with catastrophic destruction of the Colorado delta resulting.
• Climate change will transform all assumptions about water in the Southwest, especially its effect on snowmelt, both in the Rockies feeding the Colorado River, and the Arizona mountains whose snow charges the lakes of the Salt River Project. There will be less water and higher temperatures. We have no historical roadmap for what this will mean, especially because, as Ed Abbey would say, one has established a city where no city should be.
• Groundwater loss is serious in parts of the state. Nobody talks about this. Little groundwater even exists in Mohave Country, yet builders were out there platting exurban Vegas before the crash and no doubt hope to continue.
• Technological magic will only go so far. The open CAP ditch is a highly inefficient way to move water through the desert already. Taxpayers are not going to pay to raise the walls, much less build a second canal — even if enough Colorado River water would be available. Nor will the capital exist to build the magical desalination plant that has long been discussed. Much of the techno-magic thrown around is sheer hokum. The reality is that the architects of the 100-year-supply chimera just assumed they would be dead before the bill came due.
The bottom line is that sprawled, single-family house subdivision urban Arizona is not sustainable, much less one adding a million people or doubling in size or whatever the latest boosterish nonsense is peddled. The business model of population growth won't work. Even before the consequences of climate change came roaring at us, the United Nations warned of the destabilizing effects of water shortages in the 21st century. The geezers out on their championship golfcourses assumed this meant brown people in the Third World. Given tanned Arizona's economic and social conditions, they were right.