This pilot study explored the difference between statistical reality and pseudo-statistical sense based on the theory of pluralistic ignorance. Seventy-seven patients were surveyed to measure their perceptions, attitudes, and behaviors regarding tap water. Tap water in Korea is generally safe for drinking according to governmental documents; however, many people worry about the safety. Patients were selected as sample because they are usually more interested in health issues. We found pluralistic ignorance in the patients`` perceptions on experiences related to tap water. They thought other people would have experienced more bad things of tap water than they had done. There is no statistically significant difference between male and female group in the pluralistic ignorance. We also could not find any difference in attitudes toward tap water between pluralistic-ignorance group and the other. As a pilot study, this study has the limitation of small sample size. Future research on pluralistic ignorance about health issues was suggested.