SUMMARY
Improving water and energy efficiency in buildings is one of the best ways to reduce greenhouse gas emissions. This study examines various energy-related carbon dioxide (CO2) reduction measures, including the use of water efficient showerheads and shower drain water heat recovery, in order to distinguish the significance of user influence on the water usage of a shower. The probability of taking a hot shower and the number of showers taken by an occupant per day, which can be evaluated from open literature data, are used as the parameters of user responses to water conservation measures in this study. A Monte Carlo model of water consumption and CO2 reduction for showering is adopted to determine the contributions of user responses. The results demonstrate that the influence of users on CO2 reduction is significant and compatible to the influence of water efficient showerheads. This study can be used as a reference to enhance water and energy incentives and to facilitate continuous improvement in building water systems.