Water and Policy in Colorado

As the saying goes: "Whiskey's for drinking, water is for fighting." This is not far from the truth in Colorado! Water use and water rights are prominent issues in the state. It is an unusual experience for anyone that grew up on or near the East Coast, where the issue of water rights almost never comes up, to move to Colorado and find out that the "average" person is conversant in water rights. Water is such an important issue for Coloradans (and many who live in the western United States) because it is relatively scarce. As you can see in the maps below, most of the state receives under 20 inches of precipitation per year, and in fact, the average rainfall across the state is 15 inches per year, according to Denver Water. This makes most of the state semi-arid, which means that it is climatologically not far away from a desert (arid) environment. As a point of comparison, most of the land east of the Mississippi receives more than 35 inches per year, with State College, PA receiving about 40 inches per year. 

Figure 10.7: Average annual precipitation in the U.S.  Purple areas receive over 100 inches per year, dark green receive 50 - 100 inches per year, light green receive 25 - 50 inches, yellow are 20 - 25 inches, brown is 5 - 20 inches, and red is less than 5 inches per year. Larger map image available here. 

Credit: WIkimedia file: Average precipitation in the lower 48 states of the USA

Figure 10.8: Average annual precipitation, Colorado. As you can see, Denver receives about 15 inches per year. Most of the state receives under 20 inches per year, the only exceptions being some areas in the mountains. 

Credit: Wikipedia File: Average precipitation in the lower 48 states of the USA, edited by D. Kasper

Further complicating matters is the comparison of the rainfall and population geographies of the state. Recall that the Western Slope of Colorado lies west of the Continental Divide and the Eastern Slope (including the Front Range) to the east. According to "Water Law" (Denver Water), 10 percent of the state's residents live on the Western slope, but it contains 33 percent of the state's land and 70 percent of its water. Because of this, Western Slope water is often used on the Eastern Slope. This, in addition to relative scarcity and Colorado water laws, has contributed to water being a major issue in the state.