This report summarizes results for a three-year study of a single-family home in Key Largo, Florida, supplied by dual water sources, i.e., rooftop rainwater and utility-supplied water for both potable and non-potable uses. The rainwater harvesting system incorporated a water treatment system for potable uses. The study measured captured rainwater and use, utility water consumed, and reduction in stormwater runoff. The excess rainwater was directed to a spreader swale for underground infiltration resulting in zero runoff. Over a three-year period, the system captured 108,500 gallons (72%) of all rainwater (150,500 gallons) that fell on the single-family roof. As a result, utility water consumption was reduced to 33.9 gallons per capita per day (gpcd), compared to the utility average of 107 gpcd. Total water consumption (utility water plus rainwater) was 83.6 gpcd, still below the utility average, but greater than that of water-conserving homes, due in part to increased rainwater consumption when the rainwater storage tank was full. The initial capital, maintenance and life-cycle costs were documented.
Current and projected life-cycle-costs per gallon of treated rainwater are compared to utility. It is concluded that a well-designed and maintained rainwater harvesting system can 1) significantly reduce the amount of water required from a public utility; 2) deliver very high quality water that exceeds the U.S. Environmental Protection Agency (EPA) Drinking Water Standards at a competitive price; and 3) result in zero stormwater runoff. This rainwater harvesting demonstration project is expected to inspire investment in the modern revival of this ancient practice by governmental entities, philanthropists and homeowners.