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Water Law

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.

Other Topics

Rain barrels

State legislation passed in 2016 allows for the use of rain barrels at single-family homes or attached multi-family homes with four or fewer units from rooftops. 

The law allows up to two rain barrels with a combined storage capacity of 110 gallons. Depending on the amount of precipitation in any one year, a household could save between 1,300 – 2,100 gallons of water per year.

Rain barrel use is allowed under the following circumstances:

  • Water collected cannot be used for drinking.
  • No more than two rain barrels with a combined storage capacity of 110 gallons or less may be used.
  • Precipitation is collected from the rooftop of a building that is used primarily as a single-family residence or a multi-family residence with four or fewer units.
  • The collected precipitation is used for outdoor purposes including irrigation of lawns and gardens.
  • The collected precipitation is used on the residential property on which the precipitation is collected.
  • Rain barrels must be covered on the top to control insects (mainly mosquitos).

A common interest community or homeowners association may impose reasonable aesthetic requirements that govern the placement or external appearance of a rain barrel.

The Colorado Division of Water Resources (Office of the State Engineer) has additional information about the rain barrel legislation. You can also contact them at 303-866-3581.

Rain barrels are commonly found at your local hardware or home improvement store or through a search on the internet.

Graywater use

Under current Colorado law, House Bill 1044, graywater may be captured and reused only in areas where the local governments have adopted an ordinance approving the use of graywater.

The City and County of Denver Board of Environmental Health has approved regulations regarding graywater reuse. That means graywater systems may be installed and operated within the City and County of Denver. Other cities and counties in Colorado have not approved graywater ordinances or regulations; please check with your local government before installing and operating a graywater system.

Before considering graywater reuse in Denver, please review Colorado’s Graywater Control Regulation and Denver's Board of Environmental Health Rules and Regulations Governing Graywater Treatment Works.

Graywater is water discharged from showers, clothes washers and sinks. Graywater does not include water from toilets, urinals, kitchen sinks, dishwashers, or non-laundry utility sinks. Graywater also must be collected in a manner that minimizes household wastes, human excreta, animal or vegetable matter, and chemicals that are hazardous or toxic.

House Bill 1044 authorizes the Colorado Department of Public Health and Environment to develop regulations to ensure graywater can be reused safely. The bill also allows local governments to use those rules to establish graywater use within their jurisdictions. The health department has approved Regulation 86: Graywater Control Regulation, and the 2015 Colorado State Plumbing Board Rules allow for the use of graywater.

Denver Water supports graywater legislation and has worked closely with state and local agencies to make sure regulations and ordinances address the importance of keeping graywater completely separate from the drinking water system.

Once cities and counties that oversee customers located within Denver Water’s service area have adopted ordinances approving the use of graywater, Denver Water will research the best way to promote graywater use, which may include offering incentives or rebates.

For more information, contact the Colorado Department of Public Health and Environment.

Does Denver Water sell water to other states, such as California?

Denver Water does not sell water outside the state of Colorado. No one else sells water to California either, because it is not permissible to sell Colorado’s water outside the state.

The water that flows from the Colorado River to California was allocated under the 1922 Colorado River Compact, which is an agreement among the upper basin and lower basin states about how to allocate water in the Colorado River. Each state was allocated a portion of the river’s flow, and those states that did not take all the water they were entitled to had their rights preserved forever. (Normally, under western water law, if one doesn’t use the water to which he/she has rights, those rights can be taken away.)

Because Colorado didn’t have enough demand in 1922, it did not (and still does not) take its entire share of water to which it was entitled. California, however, has taken more than its share for many years. Recently, the U.S. Department of the Interior moved to stop California from taking more than its share. That water is being held in a reservoir on the lower Colorado River now. The compact was affirmed by Congress and is a part of federal law now. It can only be terminated by an act of Congress and with the unanimous consent of the compact states.