# Seismic Reliability Assessment of Water Supply Systems Considering Critical Paths
## 4 Conclusions  
This study performed a water supply reliability analysis based on critical path pipelines in an effort to improve the reliability of the water supply system during earthquake disasters. To this end, the REVAS.NET model, which calculates seismic reliability using hydraulic water supply characteristics, was used, and the impact of seismic reinforcement of pipeline sections in terms of an increase in the reliability of the water supply was examined. Nine critical paths for seismic reinforcement in an industrial water supply line in Korea were analyzed, and the relationship between increased reliability and the physical and hydraulic characteristics of each path was assessed. In order to not only increase the hydraulic supply, but also to evaluate the economic feasibility of earthquake resistance, the cost of replacing the target areas with earthquake-resistant pipe was calculated and compared with the reliability results.  
In conclusion, a strategy for ensuring the earthquake resistance of water supply pipelines in preparation for an earthquake should be determined by comprehensively considering the reliability of the water supply, the amount of supply by section, and the cost of earthquake resistance. The reliability of water supply is especially affected by the physical characteristics (pipe diameter distribution, pipe length, and connectivity) of the target section, as well as the water quantity demand of the pipeline, which has a direct influence on reliability. In addition, the construction cost associated with installation of earthquake-resistant pipes increases as the size of the pipe diameter increases, but so does the reliability due to seismic reinforcement. Therefore, it is necessary to establish a seismic reinforcement strategy by taking into consideration both economic feasibility and pipe diameter distribution. The results of this study are expected to be used to establish detailed strategies for preliminary reinforcement against earthquakes based on critical paths rather than all or individual pipelines in water supply network systems.  
In this study, critical paths were identified and analyzed such that all individual pipelines in the entire target system were included in a path. In the future, relatively long critical paths should be subdivided into second- and third-order hierarchical networks by taking phase relations into account, and the system should be re-analyzed. In particular, in critical paths that combine the main pipeline and sub-pipelines, research on the preparation of detailed establishment and reinforcement strategies should be conducted. In addition, in this study, an analysis was conducted on an industrial system in which each customer was equally affected by interruptions in the water supply. However, additional research on selection and analysis of critical paths for residential water supply areas that include higher priority consumers, including hospitals, government offices, etc., should be conducted.  
**Funding:** This work was supported by the Korea Environment Industry and Technology Institute (KEITI) through the Intelligent Management Program for Urban Water Resources Project, funded by the Korea Ministry of Environment (MOE) (2019002950002).  
**Conflicts of Interest:** The authors declare no conflict of interest.