A Design Method for Storage Capacity of Rainwater Harvesting Considering Economic Effectiveness

Abstract

The use of rainwater harvesting facilities is increasing in accordance with national laws, institutional regulations, and administrative support from local governments in Korea. However, most of the plans for storage capacity of rainwater harvesting are characterized by institutional constraints and determined by the judgment of engineers. This study aimed to suggest a method for economically determining the storage capacity of rainwater harvesting. The study presented a mass balance equation that can evaluate rainwater reuse amount according to the size of rainwater harvesting, and then defined the cost and benefit factors for the installation and operation of rainwater harvesting. Net present value (NPV) and benefit–cost ratio (BCR) were used to analyze the economic effectiveness for each storage capacity of rainwater harvesting. The proposed method was applied to the rainwater harvesting in Cheongna District in Incheon, and the NPV was found appropriate for the evaluation of the economic effectiveness. According to the design report, for the rainwater harvesting planned to be 6,740 m<sup>3</sup>, the NPV was calculated to be −478 million KRW for a 30-year design life. Meanwhile, the optimal size considering economic effectiveness was 2,000 m<sup>3</sup>, and the NPV of the size was analyzed to be +1,738 million KRW. Therefore, economic analysis is suitable as an alternative to determine the appropriate size of rainwater harvesting.