Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China's River Network Plain

Revealing the inherent relationship between urban water systems and carbon emissions has important theoretical and practical significance for promoting "water conservation and carbon reduction" in cities. This study utilizes the 2021 social water cycle statistical data of Yiwu City to quantify the carbon emissions of urban water systems. It analyzes the "water-carbon" related characteristics and carbon emission intensities under different water sources and stages and explores the carbon reduction potential of urban water systems under different scenarios. The results show that the operational phase is the main contributor to the carbon emissions of the urban water system in the research area, accounting for approximately 86% of the total carbon emissions. Over the entire process, the carbon emissions from the water supply and drainage stages are the largest, accounting for 39% and 31% of the total carbon emissions, respectively. In terms of carbon emission intensity, the carbon footprint of the water cycling process using reclaimed water as the water source is higher than that of high-quality water and conventional water sources. This is primarily due to the significantly higher carbon emission intensity in the reclaimed water phase compared with the other phases. In terms of influencing factors, the differences in the "water-carbon" correlation characteristics of different links in the water system in the research area are mainly affected by changes in urban water consumption, water treatment methods and processes, and other related factors. For the coordinated development of "water conservation and carbon reduction" in urban areas, future efforts should focus on improving the reuse rate of reclaimed water in urban life and industry, reducing the leakage rate of water distribution networks, and enhancing water treatment processes. These measures aim to increase water efficiency in urban water systems and reduce carbon emissions.