Arapahoe County, CO Landscaping Rules: Rainwater Harvesting (2026)

Colorado's water law is governed by the Prior Appropriation Doctrine (CO Constitution Article XVI §5-6), the strictest water-rights system in the U.S. Historically, all precipitation was tied to downstream water rights holders, making unpermitted rainwater collection illegal. HB 16-1005 (2016) created the limited residential exception: single-family residences and multi-family up to 4 units may collect rainwater in two rain barrels with combined capacity not exceeding 110 gallons. Collected water may only be used for outdoor purposes on the same property—lawn, garden, landscape irrigation. Indoor use is prohibited. Commercial properties, larger multi-family buildings, and industrial users require a water right or substitute water supply plan approved by Colorado Division of Water Resources. Cherry Creek Reservoir and watershed receive heightened protection under 5 CCR 1002-72, which may further restrict collection affecting reservoir inflows in some cases. Arapahoe County residents purchase water from Denver Water, Aurora Water, Centennial Water and Sanitation, Southgate, and other providers—all following 2-day/week irrigation schedules during summer. HB 19-1050 protects xeriscape and HB 21-1052 protects water-smart landscaping in HOAs.