Rainwater Collection in Colorado

The information provided is based primarily on language in Colorado House Bill 16-1005 and is intended to inform citizens on how to properly use rain barrels in accordance with Colorado law.

Rainwater collection, also called rainwater “harvesting” is the process of capturing, storing and directing rainwater runoff and putting it to use. Water from roof gutter downspouts is usually directed onto landscaped areas and is incidentally consumed by plants, but this form of use is not regarded as rainwater harvesting.

Colorado residents should understand that water rights in Colorado are unique compared to other parts of the country. The use of water in this state and other western states is governed by what is known as the prior appropriation doctrine. This doctrine of water allocation controls who uses water, how much water may be used, the typed of uses allowed, and when those waters can be used. A simplified way to explain this system is often referred to as the priority system or “first in time, first in right.”

Rain barrel use under HB16-1005:  Under House Bill 16-1005, rain barrels can only be installed at single-family households and multi-family households with four (4) or fewer units. A maximum of two (2) rain barrels can be used at each household and the combined storage of the 2 rain barrels cannot exceed 110 gallons. Rain barrels can only be used to capture rainwater from rooftop downspouts and the caputred rainwater must be used on the same property from which the rainwater was captured, for only outdoor purposes, including to water outdoor lawns, plants and/or gardens. Rain barrel water cannot be used for drinking or other indoor water uses.

It is important for rain barrel users to understand that the capture and use of rainwater using rain barrels does not constitute a water right. HB16-1005 includes language that could result in the State Engineer curtailing the use of indiviual rain barrels if a water right holder can prove that those rain barrels have impacted their ability to receive the water that they are entitled to by virtue of their water right.

How much irrigation could I expect to accomplish with rain barrels?  Each time you collect the maximum 110 gallons of water allowed in rain barrels, you can adequately irrigate approximately 180 square feet (a bit smaller than a 15 foot by 15 foot area) of vegetable garden or lawn area with the captured water. This estimate is based on CSU Extension recommendations to water lawns and vegetable gardens with about 1 inch of water during each irrigation cycle. However, a typical rain barrel user can only expect the rain barrels to completely fill aobut 10-15 times during the growing season, while vegetable gardens and lawns need to be irrigated at least twice as times per year depending on watering practices. Thus, supplemental irrigation will still be necessary to maintain a healthy lawn and vegetable garden.

For addtional information on the Colorado State University Extension Fact Sheet No. 6.707, please visit:  http://extension.colostate.edu/topic-areas/natural-resources/rainwater-collection-colorado-6-707/