Where Colorado Water Goes

Colorado is the only state in the continental U.S. with all major waterways originating within its boundaries. Water flowing out of the state travels to the Atlantic or Pacific oceans depending upon which side of the Continental Divide it originates. On average, 10,434,000 acre-feet of water leaves the state each year. Most of that water, 43%, leaves the state via the Colorado River. In fact, 75% of all the water in Colorado is found on the western slope. However, most of the population and water demand is on the east slope. This necessitates the need for trans-basin diversions from the west slope to the east slope. Approximately 475,000 acre-feet is transferred from the Colorado River basin to the east slope each year. Denver Water customers use an average of 105,000 acre-feet of west slope water per year.

Several interstate compacts regulate how much water needs to flow from Colorado to downstream states. These compacts include the: 1) Colorado River, 2) South Platte River, 3) Rio Grande River, 4) La Plata River, 5) Republican River, 6) Costilla Creek, and 7) Arkansas River.

Two inter-state compacts affect Denver Water customers. The first is the Colorado River Compact (1922) and the second is the South Platte River Compact (1925). Both of these compacts settled disputes over water rights between states and are still adhered to today.

The Colorado River Compact of 1922 divided the Colorado River into upper and lower sections. The dividing point is Lee’s Ferry, which is located near the Utah and Arizona state lines. The compact requires that the upper basin states deliver 75 million acre-feet of water to the lower basin over each successive ten-year period. The South Platte River Compact of 1925 settled disputes between the states of Colorado and Nebraska. This compact determines the amount of water that must flow from Colorado to Nebraska.