This study is designed to measure the durability of a water-repellent, which is used for treating a wooden bath or bathroom exposed to soapy water. Sometimes, the wooden bath is exposed to hot and alkaline water for long periods of time. The durability of the water-repellent is measured by examining the changes surface free energy by contact angle, chemical variation by FT-IR and surface morphology by SEM, hot water temperatures and varying lengths of exposure to alkaline conditions. For the specimen treated by water-repellent, according to the result obtained from contact angle analysis, the surface of sample was found to be non-polar. After dipping in alkaline liquid, the polarity of the surface of the sample increased with increasing dipping time. Therefore, the contact angle for diiodomethane, being a non-polar liquid, exhibited little change. In the test using low alkaline conditions, the water-repellent showed no chemical or mechanical surface variation for 7 days at pH 7 and at a temperature of 80 ℃. In the test using highly alkaline conditions, the water-repellent exhibited a change in its surface polarity value at pH 13. However, in spite of the change in its surface polarity value, the durability of the water-repellent remained constant. The results of the FT-IR and SEM tests showed no variation in the chemical and mechanical properties of the surface of the water-repellent, which was subjected to low alkaline conditions for a period of 7 days and at a temperature of 80 ℃.