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

Rainwater harvesting in Denver is regulated by Colorado state water law, which historically prohibited all rainwater collection under the Prior Appropriation Doctrine enshrined in the Colorado Constitution. HB 16-1005 (2016) created a narrow exception: residents of single-family and up to 4-unit residential properties may collect rainwater from rooftop downspouts into a maximum of two rain barrels with a combined capacity not exceeding 110 gallons. Collected water may be used only for outdoor purposes (lawn/garden irrigation) on the property where collected — no indoor use, no potable use, no sale or transfer. Larger cistern or rooftop collection systems remain illegal without a decreed water right or an approved substitute water supply plan through Colorado Division of Water Resources, which is rarely granted for residential use. Denver Water (the municipal water utility serving ~1.5M people) actively enforces through its Service Rules and educational campaigns. Commercial rainwater harvesting requires water court approval. Denver Water also administers rebates for high-efficiency irrigation, toilets, and WaterSense fixtures.