Rainwater collection or harvesting from residential roofs became legal in Colorado in 2016.
Under the rules people are allowed a maximum of two rain barrels with a combined capacity of 110 gallons at each single-family house or multi-family unit of four or fewer units. Collected rainwater may be used only for landscape uses on the property from which it was collected. The CSU Extension Fact Sheet called “Rainwater Collection in Colorado” gives a good summary of the rules.Rainwater Collection in Colorado CSU Ext.pdf
Additional resources concerning water collection or harvesting may be found through the Colorado Stormwater Center and Colorado Division of Water Resources.
SB 09-080 allows rural residents that qualify for “exempt” wells to collect rainwater with a Rooftop Precipitation Collection System Permit from the Colorado Division of Water Resources. Though these collection system permits do not limit the size of the rain barrel, the water must be collected from the roof of the primary residence and the rainwater may only be used for the uses allowed under the resident’s exempt well permit. For example, if the well permit allows for household uses only, then the rainwater could only be applied to non-potable uses in the residence; if the well permit allows for household uses and outdoor uses including lawn and garden irrigation and/or animal watering, then the rainwater could also be used for those uses. Information about SB 09-080 can be found in the "Stormwater Collection in Colorado" referenced above or through the following:DWR Rainwater Collection Information Table.pdfRainwater Collection on Properties with Residential Wells Fact Sheet.pdf
Colorado HB 16-1005 Residential Precipitation Collection2016a_1005_signed.pdf
Colorado SB 09-080CO SB 09-080 Summary.pdfCO SB 09-080 Act.pdf