Performance of Rainwater Harvesting Systems in the Southeastern United States

Due to recent concerns over the environmental impact of stormwater runoff and increased water demands, interest in rainwater harvesting systems has developed in humid, well developed regions, such as the southeastern United States. In order to better understand the anticipated usage and reliability of rainwater harvesting systems in the southeastern United States, a monitoring study was conducted at 3 rainwater harvesting systems in North Carolina, measuring cistern water levels and rainfall. Results of the monitoring study showed that the rainwater harvesting systems were typically underutilized. Water usage was most consistent at the location where harvested rainwater was used to flush a toilet; however, the water level within the cistern only dropped below 80% of capacity on one occasion during the 30 month monitoring period. A computer model was developed to simulate the performance of rainwater harvesting systems based upon historical rainfall data and anticipated usage by evaluating a daily or hourly water balance. The rainwater harvesting computer model was used to simulate the performance of a 55-gallon (208 liter) rain barrel commonly used by homeowners in this region to meet household gardening demands. A variety of turfgrass irrigation scenarios were examined, varying the size of the irrigated area and contributing rooftop. Simulation results showed that the rain barrel was not able to adequately meet irrigation demands. The low volume of water the rain barrel was able to supply for irrigation and the large amount of overflow indicated that the rain barrel was not able to effectively utilize the potential water supply coming from the rooftop and provided minimal runoff volume reduction.