The CO2 Emission Factor of Water in Japan

From the viewpoint of combating global warming in Japan, measures to reduce emissions from the activities involved in daily life have been accelerated in concurrence with the efforts made in the industrial sector to save energy. As one such measure, the reduction of energy consumption in waterworks and sewer systems by reducing the volume of water used in the housing sector is gaining attention; measures for the conversion of water saving into CO2 reduction credit in the domestic credit system are also being examined. To address the credit development for CO2 reduction by water saving, it was necessary to determine the CO2 emission factor for water. Hence, we calculated the CO2 emission factor of water use in Japan and determined the value to be 0.376 kg CO2/m(3) which applied the generating end electricity value. In addition, since electricity contributes to 90% of the energy consumption of the waterworks and sewer systems of Japan and since the emission factor for electricity changes with the power source composition ratio, the CO2 emission factor for water also needs to be updated to match the emission factor for electricity. We therefore developed a calculation equation for updating this emission factor.