The Circular Water Economy is a strategic approach to water management designed to minimize waste and greenhouse gas (GHG) emissions while maximizing resource use efficiency and safeguarding the natural environment throughout the water cycle. It involves reimagining water flows and utilization, emphasizing reuse, and recycling to foster a sustainable and resilient water system. By embracing the interconnectedness of natural and human systems, the Circular Water Economy aims to overhaul conventional linear water systems into regenerative and resource-optimized systems that not only enhances water security and environmental conservation but also contributes to economic prosperity.

Freshwater security encompasses the critical goal of ensuring consistent access to safe and ample freshwater resources for both human and ecosystem requirements, especially in the face of changing environmental conditions (e.g., climate change and socioeconomic development) that influence the availability, quality, sustainability, and resilience of water supplies. This multidimensional concept calls for integrated strategies, collaborative efforts among stakeholders, and sustainable management practices to safeguard the availability and quality of freshwater resources for present and future generations.

The urban water cycle encompasses the complex journey of water flow as it moves through natural and human-made systems within urban areas. It includes stages such as drainage, delivery, usage, treatment, and disposal. This cycle is intricately connected to natural streamflow, groundwater recharge, water supply, distribution, consumption, wastewater generation, treatment, and reuse. It’s influenced by factors like population growth, urban development, climate variations, investments in water infrastructure, conservation efforts, and regulatory frameworks for sustainable water management. Moreover, the urban water cycle is intertwined with energy production (such as cooling processes), food processing and consumption, and transportation through interdependent infrastructure systems within urban settings. Understanding these interactions is crucial for implementing integrated and sustainable water management practices in urban areas.

Water and ecosystems are closely intertwined, with water playing a fundamental role in shaping and sustaining diverse types of ecosystems. This interconnected relationship highlights the complexity of their interaction and underscores the critical need for integrated water resources management. Such approaches must prioritize ecological health, biodiversity conservation, and human well-being. This research area delves into studying vulnerable ecosystems like wetlands, conjunctive surface and groundwater systems, oases, deltas, and others. Furthermore, it focuses on harnessing naturally-based systems for water storage and for preserving water quality.

Water and energy are deeply intertwined, each playing a crucial role in the other’s functioning: water is indispensable for energy production, while energy is vital for water treatment, distribution, and management. Recognizing and managing the interdependencies, which encompass both tradeoffs and synergies, between water and energy is essential for fostering sustainable development, optimizing resource efficiency, and ensuring environmental stewardship. Employing integrated approaches to water and energy management, coupled with the adoption of efficient technologies and practices, can effectively enhance the utilization of these essential resources while mitigating adverse impacts on ecosystems and communities. This research area also encompasses the assessment of hydropower’s role within a diverse energy system that includes sources like solar, wind, and thermal energy, as well as exploring the intricate relationship between water and bioenergy development, including understanding the water requirements for biomass production and biorefinery processes, and leveraging the water quality benefits associated with utilizing cellulosic energy grasses.

Water and food security are critical aspects of human well-being and sustainable development. Water and food security are interconnected, as water is essential for agricultural production, food processing, and cooking. Implementing sustainable water management practices, such as adopting efficient irrigation techniques, promoting rainwater harvesting, and encouraging water reuse in agriculture, plays a pivotal role in bolstering food security. Furthermore, tackling water-related challenges like scarcity, pollution, and the impacts of climate change is essential for ensuring enduring food security and establishing resilient food systems capable of withstanding environmental and socio-economic pressures. These efforts can be addressed at various scales, including local, regional, and global levels, through strategies such as managing virtual water flows.

Water and health are closely intertwined, with access to clean and safe water playing a fundamental role in promoting human health and well-being. Overall, ensuring access to clean and safe water, promoting proper sanitation and hygiene practices, and addressing water-related health risks are crucial for protecting public health, reducing disease burdens, and achieving sustainable development goals related to water and health. An important consideration is the public health impacts and physiological barriers associated with the reuse of reclaimed wastewater.

The Critical Interdependent Infrastructure Systems (CIIS) encompasses the water infrastructure system and other interconnected water-related infrastructure and systems crucial for supporting diverse sectors, services, and societal activities. The interconnected vulnerability and resilience of each system within CIIS mean that disruptions in one system can propagate into others, potentially causing the failure of the entire system. Adopting integrated approaches to planning, designing, operating, and maintaining CIIS is essential for enhancing resilience and sustainability, particularly in the context of more frequent and intense extreme events and compounding effects in both urban and rural settings.

Water extremes and hazards comprise a variety of natural events and phenomena related to water that can present risks and challenges to human societies, infrastructure, ecosystems, and economies. These include hurricanes, floods, droughts, heatwaves, sea-level rise, seawater intrusion, hypoxia, water contamination disasters, and more. Managing water extremes and hazards requires a comprehensive approach that includes risk assessment, mitigation measures, preparedness planning, technology and infrastructure enhancements, ecosystem-based strategies, public awareness initiatives, and policy interventions. These efforts aim to enhance resilience, reduce vulnerabilities, and promote sustainable water management practices in the face of evolving environmental conditions.