New Rainwater Collection Law in Colorado

As of this summer, it is LEGAL for Colorado homeowners to harvest rainwater!  In August 2016, Colorado House Bill 16-1005 went into affect allowing the collection of rainwater by homeowners.

Quick Facts

  • Single-Family residence or a multi-family residence with four or fewer units are allow use rain barrels to collect rainwater.
  • A maximum of two rain barrels with a combined storage of 110 gallons or less are allowed at each household.
  • Collected rainwater may be used to irrigate outdoor lawns, plants or gardens.
  • Untreated rainwater collected from roofs is not recommended to drink
  • Experts calculate that the typical rain-barrel user can expect the 110 gallon containers to fill about 10-15 times in an average growing season
  • 110 gallons will irrigate approximately 180 square feet of garden, lawn or plants in a greenhouse

Calculating runoff from a Roof (or other Impervious Surfaces)

Simple equations can be used to determine how much rainwater your home or greenhouse could harvest.

One of the simplest ways to calculate the Possible Volume of Runoff from a Roof is the following equation:

Catchment Area (ft2 ) x Annual Rainfall (ft) x 7.48 gal/ ft3 = Maximum Runoff (gal)

Here is how we calculated the maximum annual runoff collection at Build.Sow.Grow’s greenhouse in Crested Butte, Colorado:

Greenhouse Roof Area = 264 sqft

Annual Precipitation (rain) in Crested Butte, CO = 24.09 inches or 2 feet
(You can find your local annual precipitation rates here)

264 (sqft) x 2 (ft) x 7.48 (gallons/cubic ft) = 3,959 gal/year

That is a total of 3,959 gallons of rain water annually!  

This is a fantastic amount of fresh water that can be used to help irrigate gardens!

A more in-depth series of calculations to determine runoff can be found here, and if you would like more information about rainwater harvesting,  Brad Lancaster’s “Rainwater Harvesting” series of books are an excellent resource.

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 captured 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 individual 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.

There is a lot more great information and FAQ’s on the Colorado State University Extension website.

Build.Sow.Grow. is very excited about this progress in legislature.  House-Bill 16-1005 now gives Colorado growers a chance to use excess rainwater throughout the year without expending extra resources and energy.  We are greatly looking forward to being able to incorporating a rain catchment system on all of our greenhouses.  If you would like help designing and installing a rainwater collection system for your home, contact Build. Sow. Grow. to design and/or install your rainwater collection system.