Rainwater Harvesting Experiences in the Humid Southeast USA

Due to recent concerns over the environmental impact of stormwater runoff and increased water demands, interest in rainwater harvesting systems as an innovative stormwater treatment practice has developed in humid, well developed regions, such as the southeastern United States. Rainwater harvesting systems are designed to capture runoff from rooftops. The captured water can be used as an alternative to municipal or well water for non-potable applications. The water can be used for irrigation, vehicle washing, toilet flushing, and other non-potable uses. Harvested water can potentially be used for potable uses with proper treatment. Water harvesting systems can reduce peak flows and pollutant loads as well as conserve valuable resources. 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 5 rainwater harvesting systems in North Carolina, measuring cistern water levels and rainfall. Harvested water was used for a variety of applications including vehicle washing, irrigation, and toilet flushing. In order for water harvesting to be a viable solution for stormwater management the harvested water must be used between storm events. The system must be drained as much as possible to provide storage and peak flow mitigation for the next storm event. 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. Research showed that the harvested water may require a dedicated use for water harvesting to be an effective stormwater management tool.