A water purifiers for home-use has been popularly used as increasing distrust of the drinking tap water in views of safety. Besides, chlorination of drinking water can produce trihalomethanes known as a carcinogens. In general, a water purifier is known to remove risk factors such as infectious microorganisms, harmful chemicals and heavy metals. We compared the change of water components before and after purification by a water purifier and evaluated the results whether this purification system is reliable or not for safety of drinking water. The samples of water from 11 sites at the campus of Jeju National University were examined by physicochemical analyses, including concentration of sodium, potassium, chloride, residual chlorine, boron, nitrate nitrogen, sulfur, hexavalent chromium, copper, iron, aluminium, silicon, selenium, vanadium, manganese, molybdenum, nickel, arsenic, antimony, zinc, cadmium, lead, strontium. Microbiological analysis was performed by counting mesophilic bacterial colonies. Almost of all the physicochemical components after purification were shown to decrease tendency of their concentrations but not significantly differenty except that of residual chlorine. Mesophilic bacterial counts after purification were shown to increase when compared to those of tap water. All the tap water was met the acceptance of requirement of drinking water, but samples of the water after purification were failed (4 from 11). After draining generous amount of water from a purifier, bacterial counts were observed to show a decreased tendency. Bacterial colonies were not detected when the concentration of residual chlorine was higher than 0.2 ppm. Although seasonal factors and maintenance condition were not concerned in this study, higher bacterial counts in purified water could cause some problems in using water purifier for home-use. Considering the results obtained, regular maintenance and care including filter change and sterilizing the reservoir are absolutely required. A further study is required to examine where the bacteria are coming from.