The semi-arid Denver metropolitan area receives an average of 15 inches of precipitation each year, which is about a fourth of what a tropical city like Miami receives. And, while about 75 percent of the state’s population is on the east side of the state, about 75 percent of the water in the state is located on the opposite side.
Colorado’s response to scarce and inconvenient water resources was to create the prior appropriation doctrine. The following are basic tenets of this legal system peculiar to the water-scarce western United States.
- Prior appropriation – The water law doctrine that confers priority to use water from natural streams based upon when water rights were acquired. Holders of senior rights have the first claim to withdraw water over holders who have filed later claims or own what are called "junior water rights." In times of shortage, water is provided in full to the most senior rights with junior rights being cut off. The Colorado State Engineer administers water in the state. Ownership of land is insufficient to convey a right to use water.
- Water right – A property right to make beneficial use of a particular amount of water with a specified priority date.
- Beneficial use – Lawful and prudent use of water that has been diverted from a stream or aquifer for human or natural benefit.
- Call – A demand that upstream water rights with junior priority dates cease diverting, so that water may be delivered to a downstream senior water right holder.
- Reservoir – A body of water used to collect and store water.
- Return flows – Water that returns to a stream after it has been used.
People who turn on their faucets in the Denver Water service area don't know whether the source of their water is the South Platte River located on the East Slope of the mountains or from the Colorado River or its tributaries on the West Slope. The Colorado Constitution recognizes no differences either, and states that "water of every natural stream… is hereby declared to be the property of the public. …"
The reason the state constitution and the courts recognize no geographic advantage in water is because water rights are a right to use water. As long as water is put to a recognized beneficial use and water is available, anyone may go to water court for a decreed right to use water.