Colorado Water Law Important Terms and Definitions

Prior appropriation

The legal framework for Colorado water regulations, including groundwater and surface water. The Prior Appropriation Doctrine, as it is known, is based on early western mining law, and follows the credo “first in time, first in right.” The Citizen’s Guide to Colorado Water Law breaks down the definition of the prior appropriation system:

  • Prior : “In times of short supply, court-decreed water rights with earlier dates (senior rights) can use water before decreed rights with later dates (junior rights) may use any remaining water.”
  • Appropriation : “Appropriation occurs when a public agency, private person, or business places available surface or tributary groundwater to beneficial use according to procedures prescribed by law.”
  • System : “The prior appropriation system provides a legal procedure by which water users can obtain a court decree for their water right. This process of court approval is called adjudication. Adjudication of a water right results in a decree that confirms the priority date of the water right, its source of supply, point of diversion or storage, and the amount, type and place of use. A decree also includes conditions to protect against material injury to other water rights.”

Beneficial use

The basis, measure, and limit of a water right. Colorado water law broadly defines beneficial use as a “lawful appropriation that employs reasonably efficient practices to place water to use.” The goal is to avoid wasting water so that as many water rights holders (i.e. the most “junior” holders) may have access to water as possible. Over time, the definition of beneficial use has expanded as the Colorado economy and culture has expanded. Recognized beneficial uses include, but are not limited to:

  • Augmentation
  • Instream flows and natural lake levels
  • Commercial
  • Domestic
  • Dust suppression
  • Evaporation from a gravel pit
  • Fire protection
  • Fish and wildlife culture
  • Wetland creation and preservation
  • Flood control
  • Industrial
  • Irrigation
  • Mined land reclamation
  • Municipal 
  • Nature centers
  • Oil and gas production
  • Power generation
  • Recreation on reservoirs
  • Recreation in-channel diversions
  • Release from storage for boating and fishing
  • Snowmaking
  • Stock watering
  • Water storage

Over appropriation

Colorado water is over appropriated. This means that more water exists “on paper” than water that physically exists. Senior water rights holders (with the earliest priority dates) will always have access to water before relative junior water rights holders. Because of over appropriation, there will always be junior water rights holders who receive no water, even in some of the wettest years. As a result, water rights with seniority are very valuable. This raises equity concerns over who holds power in the water system. 

River compacts

Colorado hosts the headwaters for several rivers, but that doesn’t mean that the state of Colorado has access to every drop in each river. Colorado has a number of agreements with surrounding states for water delivery guarantees. Essentially, states have to share water from rivers that flow across borders. The most notable river compact is that of the Colorado River, which includes the Upper Basin States: Colorado, Wyoming, Utah; the Lower Basin States: Arizona, California, New Mexico; and the country of Mexico. Each state holds “senior” or “junior” rights, and is obligated to deliver a certain amount of water to neighboring states. In drought years, these compacts get much more complicated. For more information, see our sections on drought and demand management. 


The amount of water it takes to submerge 1 acre under 1 foot of water (~325,851 gallons). One acre-foot typically will provide enough water for a family of four for a year. This term is typically used to quantify water rights. For example, a farmer may have access to 45 acre feet from the South Platte River each year. 


For more information on Colorado water law and additional factual, policy-neutral information on a variety of water resources topics, please refer to the Citizen’s Guide to Colorado Water Law presented by Water Education Colorado

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