By Mitch Tobin
ARIZONA DAILY STAR
Like a river searching for the sea, discussions about Tucson's water future inevitably meander to a crucial issue - just how big can this desert city grow before its demand for water overwhelms its supply?
Seems like a simple question.
But the answer is hardly straightforward.
Fiddle with projections about people's lifestyles, the economy's complexion and the area's use of Colorado River water in coming decades and the estimates vary as widely as people's opinions on the matter.
Although Tucson isn't on the brink of running dry, many experts say water could become a limiting factor in Tucson's growth at some point.
"Using up a nonrenewable resource within a generation doesn't make a lot of sense," said Kathy Jacobs of the Department of Water Resources' Tucson Active Management Area.
In general, as water tables drop, pumping costs increase, water quality declines, well production falls and above-ground riparian areas suffer.
Overpumping of ground water also can cause subsidence, when the earth sinks because of the removal of the water below, possibly cracking foundations.
The pitfalls of overdraft led state lawmakers to enact the Groundwater Management Act in 1980. The law's goal is "safe yield" - where demand for ground water is balanced with what nature and humans return to the aquifer. Tucson, Phoenix and Prescott are supposed to reach safe yield by 2025, but there's no punishment for failing to do so.
Current projections say Tucson is headed toward safe yield, but we won't make it by 2025. Phoenix and Prescott will make even less progress.
The Tucson area's current overdraft on ground-water supplies is 169,500 acre-feet per year. By 2025, we're expected to be down to 50,400. (An acre-foot is 325,851 gallons, about what a family of four uses each year.)
The drop is expected because of increasing use of CAP, gains in conservation and the projected 65 percent decline in agricultural acreage.
Agriculture is projected to shrink around Tucson because Arizona's water law gives cities priority over farmland, much of which uses excess CAP water that cities have not been able or willing to use yet. Developing farmland generally results in much less water use there.
Although the Tucson area's CAP use is expected to increase from 8,500 acre-feet to 162,500 acre-feet by 2025, switching users from ground water to river water faces two main obstacles - the aqueduct is inaccessible to many and CAP water is more costly than ground water.
Tucson Water's use of Colorado River water also is constrained by a 1995 law passed in the wake of CAP's disastrous debut that bans direct delivery of the water to residents.
Besides the goal of "safe yield," state law also requires Tucson property owners who want to subdivide their land to prove they have a 100-year water supply. That requirement is met if they are served by a water utility, such as Tucson Water, which has proved it has the 100-year supply.
Backers of these regulations say they force growth to rely on renewable supplies of water, but critics complain the rules are too loose, allowing utilities to get credit for ground water stored in distant basins.
Tucson's water balance will also invariably revolve around how much each of us uses.
"That runs into lifestyle issues," said University of Arizona researcher Gary Woodard.
Woodard noted several conflicting trends in local water conservation.
In recent years, Tucsonans have turned toward low-water xeriscape landscaping, but also toward swimming pools.
New dishwashers save water, but not if they're put on pot-scrubber mode.
Air conditioning has replaced evaporative coolers for many, but outdoor misters have become more popular.
"For every area we've had improvements in conservation," Woodard said, "there have been other areas where prosperity and new technology have created new water uses."
Technology might one day solve the Southwest's water dilemma, with seashore desalination plants creating a near-limitless water supply.
One member of Tucson's safe-yield task force noted that frustrated colleagues sometimes joke that "it's not that far to the Sea of Cortez. (Gulf of California)."
Today, wealthy, oil-rich Arab nations do the most desalination because it requires so much energy. But water experts say that could change in coming decades if the cost of extracting ground water or acquiring river rights escalates and technological breakthroughs make desalination cheaper.
Jacobs argues that Tucson's growth likely will be checked by factors other than water, such as traffic, air pollution and residents' quality-of-life concerns.
"I'm hoping we'll reach some natural limit in this region that's not defined by water," she said. "I'm hoping that has to do with leadership and active decision making, rather than waiting for a crisis to strike."
* Contact Mitch Tobin at 806-7739 or by e-mail at mtobin@azstarnet.com.
Find out more about the CAP at its own Web site.
Tucson Water is the delivery source for CAP water, and more.
Get the view of opponents of adding CAP water to local mains.
