Why Phoenix Exists

This is "Roosevelt Dam," a dam that holds back the water that makes up Roosevelt Lake, which provides water to a very thirsty Phoenix:

My lovely bride and I took a drive up there over the weekend just to see something new in our state. Roosevelt Lake is a fairly good-sized resevoir, though I don't have the exact specifications for it in my head. The dam was made taller about ten years ago so the level of the water and the capacity of the resevoir could be increased.

I learned recently that the unit of measure for water used for large-scale water management issues is something called an "acre-foot" of water. That's one acre one foot deep of water. According to Wikipedia, that works out to 325,851 U.S. gallons. What's interesting is that the display write-ups at the resevoir indicated that an acre-foot was what a family of four uses in one year.

That struck me as odd.

So I did the math:

• 325,851 gallons / 365 days = 892.7 gallons per day for the family of four
• 892.7 gallons / 4 = 223.175 gallons per person per day

That number is extremely high for ordinary human consumption. So what I figure is that the claim an acre-foot is what "a family of four uses in a year" is really a planning number that factors in non-consumption uses as well -- watering the lawn, filling the pool, and probably commercial and industrial uses as well. It's a way to handle the allocation of "water rights" based on an assumption about population. So it's a little like a "fixed cost allocation" -- your and my "salary overhead burden" is something like $250K, though neither of us makes anywhere near that. But our "overhead burden" includes benefits as well corporate fixed cost allocations that need to be factored in somewhere.

I read that the Colorado River provides 15 million "acre-feet" of water a year, which is allocated between California and Arizona. I've often wondered why, if water is truly scarce in Arizona, why there isn't more of a push to conserve or a pricing structure that penalizes usage above some limit. There is neither -- no real push to conserve and a price/gallon less than what I paid in Washington D.C.

Why the difference? A theory -- the allocation between California and Arizona was settled some years back after decades of litigation. What I may be seeing is the effects of a "use it or lose it" mind set. California is insatiable. It might be that Arizona is concerned that consistent under-usage of its water rights might result in a reshuffling of those allocations.

Just a guess. But a guess based on cynicism, which is usually a good way to guess.