This book reviews the latest development on carbon neutrality and carbon reduction in urban water systems at home and abroad. It proposes a systematic methodology applicable to carbon neutrality in urban water system based on a thorough study to enrich the existing approaches. It also presents both short-term and long-term carbon neutral path for the upgrade of technology. The basis of English translation of this book, originally in Chinese, was facilitated by artificial intelligence. The content was later revised by the author for accuracy.