Tapped out: Front Range cities get up to 50 percent of their water from the Western Slope, but population growth and future droughts could limit transmountain diversions or stop them altogether under the 1922 Colorado River Compact.

• Author: Best, Allen

1. STORM ON THE HORIZON

   It's been said that every glass of water in Colorado comes from the Western Slope. Strictly speaking, that's wrong. A few places--Burlington, Trinidad and Castle Rock come to mind--get no water from west of the Continental Divide.

   Yet the saying rings true, because without tunnels perforating the Continental Divide, augmenting native supplies with 400,000 acre-feet of water on average from the Colorado River and its tributaries, Front Range cities and the farms sprawling eastward would be very different places.

   Rocky Ford cantaloupes would be more scarce, corn fields near Greeley a more risky proposition, and most of the larger cities along the Front Range altogether less lush and perhaps smaller in population. Water from the Western Slope constitutes 30 percent to 50 percent of water along the Front Range in any given year.

   That's why this specter of a "compact call" on the Colorado River matters. Should Colorado be forced to curtail use of Western Slope water appropriated after 1922, most transmountain diversions would likely be limited and perhaps stopped altogether. Colorado might survive well enough for one year, even two or three. After all, while the state had a hollow-eyed look during the 2002 drought, it bounced back.

   But drought leading to a call from the lower-basin states of Arizona, Nevada and California would likely be more prolonged and possibly more intense. Continued population growth would elevate the stakes. The consequences could be dire.

   "It's not going to happen in the next five years, but we are going to have to be serious about it," says Jennifer Gimbel, director of the Colorado Water Conservation Board, a key state agency.

   The 1922 Colorado River Compact provides the trip-wire for curtailment. The agreement apportions waters of the river and its tributaries among the seven basin states. One clause specifies that the upper-basin states--Colorado, Wyoming, Utah and New Mexico--must allow passage of 7.5 million acre-feet of water annually at Lee's Ferry, at the entrance to the Grand Canyon, based on a 10-year rolling average.

   Meeting this delivery obligation was never a problem. Then came 2002--followed by several more dry years in the Colorado River Basin. Even then, downstream deliveries continued. But Lake Powell shrank--shockingly so. The West's premier splish-splash joint, Powell's express purpose is to store water necessary to meet the downstream commitment at Lee's Ferry.

   But by autumn 2005, the reservoir that had taken 17 years to fill was down by two-thirds, the canyon walls scummy with the bathtub rings of higher-water marks. A dead pool, the point below which no water can be released, looked like just another bad winter or two away.

   Instead, deep snows returned in 2006, causing rising water levels in Powell, which is now at 64 percent of capacity. Even so, the eyes of Coloradans had widened. An assistant state attorney general, James Eklund, was assigned to put the 1922 compact under a legal microscope. Many began to speculate about the potential for litigation. It's a dispute nobody seems to want.

   "We would probably have a good 15 years of litigation in the Supreme Court over these issues," says Jim Lochhead, an attorney with Holland & Hart who represented Colorado in river issues for many years. That would be an unacceptable outcome for public entities managing public resources, he says.

   Eric Wilkerson, general manager of the Northern Colorado Water Conservancy District, the state's largest diverter of Western Slope water, discounts talk of what he calls an Armageddon-type situation. Colorado, he says, has both the time and the tools to allow it to meet downstream obligations without yanking the rug from under post-1922 water-right owners on the Western Slope.

   But even if no compact call comes, water margins will erode in coming decades as Colorado and the American Southwest becomes more hot, dry and crowded.

   The Colorado Demography Office projects the state's population, now at 5 million, will grow to 7.8 million in the next quarter-century, with most of that population huddled along the Front Range. Demographers predict similar growth for the broader Colorado River system, which includes Los Angeles, San Diego and Salt Lake City. Similar to Denver, they are outside the basin but get Colorado River waters. That area's population of 30 million is...