Drinking water in Taiwan commonly comes through three major processes: (1) raw water from reservoirs, (2) treatment plants, and (3) distribution network. Some studies have shown that the water supply reliability usually focuses either on the raw water or distribution sections. In addition, high turbidity caused by intensive rainfalls usually overloads the water treatment plant and causes water supply interrupted temporarily. Therefore, the water shortage rate, vulnerability, and flexibility could be potentially overestimated if without taking account water quality. Moreover, the “reliability” was misread that most researchers only concentrated on quantity rather than quality. Both quantity and quality are the most concerns for the water consumers. Thus, this study would like to: (1) redefine “water supply reliability” as that both water quantity and quality meet up with the satisfaction of consumers; (2) develop a methodology to analyze the water supply system as a whole. In the first year, a water supply system simulation model will be developed. Synthetic flow and discharge-turbidity will be used to analyze the reliability of raw water subsystem. In the second year, availability theorem will be employed to analyze the failure probability of detail components of water treatment plants and their relations with water quality. In the third year, availability theorem will also be employed to analyze the failure probability of detail components of distribution network. The results of this study can be a very fundamental basis for the water supply administrators to improve and maintain their facilities from top to bottom, and enhance the consumer confidence in drinking water.