The influence of household rainwater harvesting system design on water supply and stormwater management efficiency

Rainwater harvesting is increasingly being recognised as a sustainable option for both urban water and stormwater management. This study explores the potential impact of household rainwater harvesting on water supply augmentation and stormwater management in a typical three-bedroom house in Newcastle-upon Tyne, NE England. The continuous simulation of historical rainfall events at 15-minutes resolution over a 30-year period (1984-2013) is carried out to evaluate the system’s water saving and stormwater control efficiencies. Current and future rainfall projections are also incorporated in the analysis. The British Code of practice (BS 8515) is adopted to design the rainwater harvesting system. Results indicate that a rainwater harvesting system which is primarily designed for water supply augmentation with the size of 2.4 m3 contributes 64% of non-potable water demand (toilet flushing) and an 86% reduction of stormwater runoff volume into the sewer system. A larger system (6.5 m3) which is sized for both water supply augmentation and flood management provides 70% non-potable water supply and 96% reduction of stormwater runoff volume, indicating that a system which is designed for water supply only may be sufficient to achieve dual benefits. The relationship between storage and system efficiencies are explored for commercially available tanks for historical and future rainfall events. The influence of storage volume on flood peak attenuation is also explored for the historical flood events.