Water homeostasis is essential for healthy living. Body water turnover, meaning the replacement of body water that is lost in a given period of time, has been examined in a number of previous studies, and a review of their results has yielded the following findings. Children up to 15 years of age show higher body water turnover than adults, although it is not clear how the aging process influences body water. Among people of similar age, the rate of body water turnover seems to be higher in those who exercise than in those who are sedentary. Therefore we hypothesized that healthy individuals have a higher body water turnover than unhealthy individuals whose metabolic balance, as indicated by water turnover, has broken down, and that a prolonged condition of excessively slow body water turnover may be associated with a lower level of metabolism. If so, body water turnover can be an indicator of human health. However, there is a paucity of information regarding water turnover rates in individuals with various physical characteristics. This study indicates the need for further investigation of body water turnover levels associated with significant changes in physiological condition and metabolic state.