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The Colorado Water Plan acknowledges the risk of future gaps between municipal water supply and demand and the need for meeting increased municipal water needs without harming other uses. The integration of residential rainwater harvesting coupled with water-wise landscaping could help reduce the supply gaps by curtailing residential irrigation demands. In this study, we used a daily water balance model to assess the performance of rainwater harvesting systems at the parcel scale in 60 urban areas across Colorado. The metric used to evaluate the performance of the system was the annual rainwater harvesting yield (from April to October), that represents the fraction of the total residential irrigation demand that is supplied by the harvested rainwater. The systems were modeled across nine precipitation scenarios (historic, future increase, and future decrease), six housing configurations (high, medium, and low density), three storage capacities (110, 300, and 500 gallons), and three irrigation demand levels (high, medium, and low) for each location. Considering all the system’s configuration combinations and locations, the simulations resulted in a range from 2% to 100% of annual rainwater harvesting yield. There were 15 urban areas that obtained a mean annual yield of over 25% considering a high-density housing with a low demand reduced irrigation area and current legal storage limit of 110 gallons. The region with the highest annual yield was found in the high elevation portion of the Interstate 70. The southern and western parts of Colorado had the lowest mean annual yield. Overall, rainwater harvesting comes out to be a promising additional water source for urban areas in Colorado, offsetting outdoor water use from municipal supplies.