This project implemented contaminants screening process of drinking water quality regulation. Six unregulated polybrominated diphenyl ethers (PBDEs) were selected for evaluation. Their concentration was monitored in six representative drinking water treatment plants, and their health risk in drinking water system in Taiwan were evaluated. Results indicated that there is no significant risk of these 6 compounds on drinking water in Taiwan. This project also collected the toxicity information and monitoring histories of unregulated contaminants in Preliminary Contaminant Candidate List (PCCL) to evaluate if the concern level of some chemicals should be increased to Contaminant Candidate List (CCL). After evaluation, concern level of NPYR and PFHxS were increased from PCCL to CCL. In addition, this project inspected 26 unregulated compounds of emerging concern in drinking water and got 3340 data in total. There were 14 compounds with monitoring results all below detection or quantification limitation. The other compounds with detection values were at very low concentration level. There were only few samples with higher concentration on germanium, boron, Geosmin, and per- and polyfluorinated chemicals (PFCs). It is suggested to monitor them continuously. Besides, this project evaluated 6 different microbial indicators at 20 sampling points in water distribution system. Only one sample detected total coliform, which may result from low free residual chlorine. Results indicated that maintain free residual chlorine is important stretagy to reduce microorganism in water distribution system. In addition, it is suggested to regulate E. coli rather than total coliform, which has less specifity. Drinking water quality data of small drinking water system in ten years were collected. High risk was found with microbial incitors. Therefore, disinfection system was suggested to implement. Regarding to the drinking water management regulation and respondences to extreme climate, this project reviewed potable water reuse cases apply in other countries. Public communication is one of key factor of successful implement except for technologies and management aspect.