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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. (See more below.)
  • 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.

More information

Water rights

First in time, first in right

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.

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 about four single-family households for a year).

About 80 percent of the water in Colorado is found on the West Slope. But about 80 percent of the state’s population live on the East Slope. That division means the growing Front Range needs to move water from the West Slope to the East Slope through trans-basin diversions. Utilities from across the East Slope transfer about 475,000 acre-feet of water from the Colorado River basin to the East Slope each year. On average, Denver Water customers use about 125,000 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.

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 mosquitoes).

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.

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.