First in time, first in right
To irrigate crops and supply domestic water, early settlers in the western half of the United States built ditches to divert water from creeks or streams that were not necessarily adjacent to their land. Most farmers and ranchers built a head gate to divert the water into a ditch, and many built small reservoirs or ponds to store their water for future use. This method of obtaining water evolved into the “first in time, first in right” basis of western water law. People who were first to file for water rights obtained senior rights. Those who filed afterward obtained junior rights and were not allowed to divert water until senior rights were fully satisfied.
Over time, water companies evolved to deliver water to cities and towns using the same diversion techniques, but to a much larger scale. Those early laws made to regulate water still hold true today. Water law is particularly an issue in Colorado, where water that flows out of the state travels to the Atlantic or Pacific oceans, depending on which side of the Continental Divide in which it originates. On average, 10,434,000 acre-feet of water leaves the state each year (one acre-foot is equal to 325,851 gallons of water and will supply slightly more than two single-family households for a year).
About 75 percent of the water in Colorado is found on the West Slope. But about three-fourths of the state’s population live on the East Slope. That division means the growing Front Range needs to move a lot of water from the West Slope to the East Slope through trans-basin diversions. About 475,000 acre-feet is transferred from the Colorado River basin to the East Slope each year. On average, Denver Water customers use about 105,000 acre-feet of West Slope water per year.
Interstate compacts
Several interstate compacts regulate how much water needs to flow from Colorado to downstream states, including:
- Colorado River Compact of 1922
- Upper Colorado River Compact 1948
- South Platte River Compact of 1923
- Rio Grande River Compact of 1938
- La Plata River Compact of 1922
- Republican River Compact of 1942
- Costilla Creek Compact of 1963
- Arkansas River Compact of 1948
Two interstate compacts directly affect river systems from which Denver Water derives its supply: the Colorado River Compacts of 1922 and 1948, and the South Platte River Compact of 1923. Both 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 any 10-year period. The South Platte River Compact of 1925 settled disputes between the states of Colorado and Nebraska and determined the amount of water that must flow from Colorado to Nebraska.
Denver Water works hard to protect and maintain its several hundred individual water rights. It monitors and enforces the terms and conditions of numerous water delivery, exchange and trade agreements to help ensure Denver Water will continue to have an adequate supply of water well into the future.