Assessment of Rainwater Harvesting Facilities Tank Size Based on a Daily Water Balance Model: The Case of Korea

Factors affecting rainwater resource management for the present and future include population growth, urbanization, and climate change. Rainwater harvesting (RWH) allows multiple urban water-related issues to be mitigated. In this study, a spreadsheet-based daily water balance model was developed to analyze the existing laws and regulations regarding the storage tank size of RWH facilities. Six buildings at different locations were selected for this study. Two are office buildings, two are school buildings, and two are sports buildings. The term “RWH facility evaluation criteria” is collectively used for rainwater supply satisfaction rate, rainwater guarantee rate, and rainwater utilization rate. A green roof can hold the rainwater for some time, reducing the peak flow and runoff volume. The results provide evidence that, among the selected studied buildings, buildings having a combination of a green roof and RWH facility score the highest in terms of RWH facility evaluation criteria, even though the actual tank size is much smaller than the standard tank size. This is the case with the Yesan County Office, in which a green roof connected to a small (66 m3) rainwater storage tank is installed. As a green roof can decrease the runoff volume, the rainwater can be managed efficiently with less pumping energy and only a small storage tank.