Last in Time: Rooftop Rainwater Collection in Colorado

Unlike the fertile land of the eastern United States, the West is arid and water has consistently been a constrained resource. Faced with a need to establish water rights tailored to these circumstances, the western States established the prior appropriation doctrine, coined “first in time, first in right.” Today, it is the law of land in most of the West. Under this doctrine, ownership of water is established through a hierarchy of titles: senior appropriators and junior appropriators. While both senior and junior appropriators’ access to water is constrained by the amount of water the environment provides, senior appropriators enjoy first access to the water. Today, the state of Colorado is debating a deceptively straightforward question hundreds of years after the introduction of this doctrine: who is the senior appropriator of rainwater falling on rooftops in urban and suburban areas?

On one hand, the foundations of prior appropriation establish that all water is subject to a claim of ownership at some point. Rainwater marks water’s introduction into the land and it eventually navigates downstream into bodies of water where water rights are likely firmly established. Under this rationale, the collection of household rainwater would ultimately harm the public because, when collected, it is no longer introduced downstream into larger bodies of water. In this view, the rainwater collector unjustifiably collects rainwater to the detriment of those downstream, including municipalities, farmers, and other water users.

On the other hand, household rainwater collection supporters emphasize that the amount of water collected through this method is minimal and does not pose serious risks for downstream users—97% of rainwater never encounters streams and is instead harvested by plants or evaporated back into the cycle. Instead, where using established household water supply lines to irrigate flowerbeds and gardens leads to an “out of sight, out of mind” perspective of the amount of water used, rainwater collection presents an opportunity for increased water user awareness. In turn, this increased awareness encourages a more individualized connection to the scarce resource leading to conservation on a micro-level.

Colorado’s Historical Approach

In 2009, the Colorado legislature began to address these questions by passing two laws related to household rainwater collection. Together, the bills allow residents of the state with private wells to collect rainwater for specific uses. These uses are limited to: ordinary household purposes, fire protection, livestock and domestic animal watering, and the irrigation of not more than one acre of gardens and lawns. Today, residents of urban areas who are connected to the city water system remain precluded from collecting rainwater in any manner, including cistern or tanks, for later use.

Other Western States’ Approaches

Colorado has not been alone in its effort to answer questions related to household rainwater collection. Until 2010 in Utah, rainwater collection required an existing water right covering the land where water was collected. However, due to public demand, today only registration with the city water authority of an intention to collect rainwater is required. Similarly, in Idaho, rooftop rainwater collection is permitted so long as the water is put to beneficial use. The landowner of property where water is collected has an unqualified right to collect the water, so long as it does not cause injury to another water user.

In New Mexico and Arizona, rainwater collection is encouraged. Santa Fe, N.M., exemplified the state’s embracing rainwater collection policy by passing an ordinance requiring the collection of a minimum of 85% of rooftop rainwater for all newly constructed dwellings within the city.

Recent Developments in Colorado

Colorado remains the last state to maintain an explicit ban for those connected to a city’s water system to collect rainwater. However, prominent water-related organizations, including Denver Water, Conservation Colorado, Environmental Defense Fund, and many others, support Colorado House Bill 15-1259. The bill allows all Colorado residents living in a single-family residence or multi-family residences with four or fewer units to collect rainwater in 100-gallon barrels, with a maximum of 600 gallons of water collected per year. The collected water must be used on the property where it was collected and applied to outdoor purposes only, such as irrigation and gardening. To illuminate the amount of water involved, advocates of the measure emphasize that the goal of collected rainwater is small in scale: 100 gallons would sufficiently water a small flowerbed or garden, but would not be sufficient to water a full lawn.

The bill, having passed the House Agriculture, Livestock & Natural Resources Committee, is currently facing heated debate in the Colorado House. Opponents argue the rainwater collection provisions amount to an effort to circumvent the existing and long-established water rights system of Colorado. Supporters, however, counter by emphasizing that the collected water ultimately ends up in the ground, available for downstream use.

Colorado Should Expand Permissible Rainwater Collection

Whether Colorado will leave its status as the last holdout and join the trend of Western states to allow, permit, or encourage rooftop rainwater collection remains to be seen. However, the existing water systems of urban areas of Colorado unfortunately allow urban citizens to maintain an inaccurate understanding of just how limited water is across the state and region. If for no reason other than increased awareness in urban communities of the limited nature of water, rooftop rainwater collection should be seriously considered. Further, because most of the water that an individual may collect through this method ultimately evaporates or is harvested by plants, allowing for a more directed use among flowerbeds and gardens does not pose unreasonable constraints on potential downstream users. Rooftop rainwater collection in Colorado presents a new opportunity for conservation that, in aggregate, may aide water rights holders by encouraging water conservation.


The title image features a rainwater collection device used by the U.S. Bureau of Land Management. This image is part of the public domain.


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