建築物使用的自來水看似十分便利，但其實必須經過取水、淨水處理、送水等流程方能送抵使用者家中，提供方便與安全衛生的用水。這些處理過程中自來水公司需要使用到各類的輸送方式與淨化水質處理措施，而這些過程均會使用到各式能源或添加處理水質所需的其他原料，間接也會排放出CO2。本研究透過生命週期評估的觀念，以台灣自來水廠的直接生產線調查法，進行本土化的自來水CO2排放量評估，我們可以換算出單位自來水的CO2排放量為0.297kg-CO2／m3（以總售水量計算）。利用上述自來水的單位CO2排放量，使得以進行建築物節約用水設計的環保評估，並能與地球環保的CO2減量完全接軌，提供政府推行永續水資源政策的參考。

It may seem extremely convenient to get tap-water in a building. In fact, to get fresh and hygienic running water in building, water need to be obtained, decontarninated and transported. The transportation and decontamination processes of water would require various energies and chemicals and would lead to the emission of carbon dioxide. This study is to evaluate the emission of carbon dioxide of tap-water in Taiwan. Based on the total water volume sold by Taiwan Water Corporation, the concept of life-cycle appraisal and direct production line survey procedure were used to calculate the emission of carbon dioxide of unit tap-water in Taiwan is O.297kg-CO2/m3. From the study, we can evaluate the water usage efficiency in a building.