Cities are dynamic systems, and the urban water systems within them can be evolved to provide water services to both humans and the environment while also enhancing the broader urban environment. This is done by embracing innovation and technological advancement while focusing on increased service to the human population and the local and broader environment. In the contemporary era, characterized by the rise of low-carbon and intelligent technologies, the swift pace of socioeconomic expansion highlights the critical need to address issues of urban water security and environmental preservation. Amid escalating resource and environmental constraints, adopting holistic blue-green-grey strategies becomes imperative for the sustainable governance of urban water resources. An integrated approach is needed to navigate the intricate challenges of urban water dynamics while fostering enhanced ecological performance and resilience.

We curated this special issue on “Sustainable Urban Water Systems” for these reasons. The issue weaves together a rich tapestry of research that not only addresses the challenges of urban water management but also envisions the future of our urban landscapes. Through this compendium of articles, we seek to reimagine the essence of urban water systems, where the synergistic combination of natural elements and engineered solutions can advance a future of resilience and sustainability. In six diverse and insightful articles, our contributors illuminate the path toward sustainable urban water systems—a journey marked by technological innovation, ecological sensitivity, and intelligent management.

Wastewater treatment takes center stage in this special issue, with a focus on cutting-edge technologies and methodologies. Wang et al. address the current status and future potential of digital twin technologies for wastewater management. Their review underscores the transformative potential of digital twins to revolutionize the design, operation, and management of wastewater treatment facilities and sewer networks, showcasing significant advancements in digital water management. Li et al. make a compelling case for the utilization of nanoscale zero-valent iron in the remediation of heavy-metal-contaminated wastewater. Their perspective article emphasizes the multifunctionality and operational benefits of this approach, positioning it as an eco-friendly solution to a pressing global environmental issue.

Three research articles in this issue report on multidimensional innovations in wastewater engineering. Ma et al. investigate microbial dynamics within coking wastewater treatment systems, focusing on the genetic mechanisms that enable efficient nitrogen removal. Yang et al. introduce a novel method for analyzing the energy-water nexus in wastewater treatment, underscoring the intricate interplay between influent characteristics and energy consumption. Wang et al. introduce a cutting-edge multimodal machine learning approach to optimize aeration in wastewater treatment plants, marking a significant advance toward low-carbon urban water systems.

Turning to water supply, Xiao et al. comprehensively summarize disinfection byproducts and their precursors in drinking water sources and explore their origins, influencing factors, and environmental implications. Their review is an essential tool for understanding water contamination and offers unique insights into managing water quality and public health.

As the global community grapples with the escalating challenges of climate change and increasingly severe rainstorms, the threat of urban flooding has intensified. Urban floods are predominantly driven by flows with increasing duration and intensity from regional flooding that raise urban water levels, disrupting drainage systems and causing extensive waterlogging. Exacerbating this issue, rapid urbanization and the expansion of impervious surfaces hasten rainwater runoff, undermining natural water absorption and storage capacities and placing excessive strain on drainage infrastructure that is inadequately equipped to handle even moderate precipitation levels. In response to these critical concerns, China has pioneered the innovative “sponge city” initiative. This visionary strategy seeks to transform urban environments into entities capable of naturally absorbing, filtering, and purifying rainwater. By integrating natural (“green” and “blue”) and engineered (“grey”) elements, this approach endeavors to regulate the volume, peak flow, and pollutant levels of urban runoff, thereby bolstering urban resilience against natural disasters. This topic warrants greater attention and is of urgent concern.

As we navigate through these diverse yet interconnected articles, we are invited to envision a future in which blue-green-grey solutions not only address today’s urban water challenges but also sculpt a resilient, sustainable, and flourishing urban water narrative for generations to come. This special issue serves as a repository of current research and a guiding light, steering us toward an integrated and forward-looking approach to urban water systems, where the fusion of nature-based and engineered solutions heralds a new era of water-wise urban development.