The increased emphasis on sustainability has resulted in an effort to reduce the reliance on municipal water in favor of the use of collected rainwater. This paper addresses the reliability of rainwater collection and use for residential buildings. It describes a procedure that utilizes a water balance based on the amount of collected rainfall, household demand, and storage tank capacity. The probabilistic nature of rainfall is incorporated by establishing weekly exponential distributions based on historical data. These rainfall distributions are used in a Monte Carlo simulation along with characteristics of the residential system (catchment area, storage tank size, household demand, etc.). Results show that along with the size of catchment area, the storage tank capacity is critical in determining the reliability of the system. The procedure is illustrated with data from Portland, Oregon.
