The GM of residual chlorine in the spray water of warm-water bidet toilet seats and in tap water was 0.04 mg/L and 0.24 mg/L, respectively, which represented a significant difference (P < 0.01). This result demonstrated that there is clearly less residual chlorine in spray water than in tap water (Table 1). Moreover, when these data were log-normalized, it became clear that artificial factors (e.g., heating) caused the residual chlorine to disappear in the spray water. However, no significant difference in the residual chlorine concentration of spray water was observed between the male and female restrooms. Residual chlorine levels were higher in the spray water from toilet seats in the outpatient building than from those in the research building (P < 0.01; Figure 1). Frequent inflow of tap water into a toilet's warm-water tank is needed to maintain the chlorine concentration in spray water; that is, the residual chlorine concentration cannot be maintained without frequent use. As such, we surmised that the toilet seats in the outpatient building were used more often than those in the research building.