Jaime Nivala: Nature-based solutions for urban water management

Challenges to Treatment of Urban Water Systems and the Potential of Enhanced Natural Treatment Solutions

Urbanization is accelerating at an unprecedented rate across the globe, bringing with it numerous challenges related to water management. A significant issue is water scarcity and water insecurity, which threaten the sustainability of cities and rural areas alike. Urban water systems are under immense pressure from increasing population densities, pollution, climate change, and aging infrastructure. These challenges not only compromise human health and wellbeing but also have detrimental effects on ecosystems, which provide crucial services such as clean air, water, and soil health.

In Europe, over 70% of the population currently resides in urban areas, and projections indicate this figure will surpass 80% by 2050. As cities grow, the existing centralized infrastructure—pumping stations, treatment plants, sewer networks—becomes increasingly strained and less resilient against the impacts of climate change. Extreme weather events such as floods, storms, and droughts are becoming more frequent, threatening to overwhelm urban water systems and result in failures, environmental contamination, and economic losses.

One of the fundamental issues in urban water management is the pollution of surface and groundwater. Urban stormwater, wastewater, and runoff often contain a complex mixture of pollutants from point sources (such as industrial discharges and sewage outfalls) and non-point sources (such as vehicle emissions, urban runoff, and land use activities). These pollutants can compromise water quality, threaten human health, and damage ecosystems, ultimately impacting land value, urban aesthetics, and residents’ quality of life.

Given these challenges, there is an urgent need to rethink traditional approaches to urban water treatment. Conventional centralized systems, while effective in many respects, often lack the flexibility, resilience, and sustainability needed to cope with the increasing demands and complexities of urban water cycles. As a response, constructed wetlands, green infrastructure, and other nature-based solutions are gaining recognition for their potential to offer sustainable, cost-effective, and multifunctional benefits.

Advantages of Applying Enhanced Natural Treatment Solutions

Nature-based solutions for water management can significantly improve water treatment outcomes by harnessing natural processes such as wetland vegetation, soil filtration, microbial activity, and ecological functions. These systems can be integrated into urban landscapes to provide multiple benefits simultaneously. For example, they can improve water quality by removing chemical pollutants, sediments, and pathogens, while also reducing flood risks through increased stormwater retention and infiltration.

Beyond their primary treatment functions, these systems contribute to mitigating urban heat island effects by greening the cityscape and increasing green cover. They also offer aesthetic and recreational value, transforming neglected areas into attractive urban green spaces. This integration of ecological features supports the goals of creating more livable, healthy cities.

From an environmental perspective, nature-based solutions contribute to the circular economy by promoting water reuse and resource recovery. Treated water can be reused for irrigation, industrial processes, or even potable purposes, depending on its quality. Such reuse reduces dependency on external water sources and alleviates pressure on limited freshwater reserves. Additionally, these systems provide ecological habitats, enhance biodiversity, and improve social inclusion by involving local communities in their planning and management.

Socially, nature-based solutions promote greater equity and social cohesion, as community members are often engaged in the co-design, implementation, and maintenance of natural treatment systems. They foster environmental awareness and stewardship, which are crucial for the long-term sustainability of urban water management strategies.

However, the widespread adoption of nature-based solutions faces several challenges. Designing, planning, and implementing these systems at scale requires overcoming technical, financial, and institutional barriers. Ensuring long-term operational sustainability and addressing potential hazards, such as chemical or biological contaminants, necessitate validated risk assessment methodologies. Financing mechanisms must be innovative and adaptable to diverse socio-economic contexts to facilitate large-scale deployment.

The MULTISOURCE project

The MULTISOURCE project (ModULar Tools for Integrating enhanced natural treatment SOlutions in URban water CyclEs, EU Grant Agreement 101003527, 2021 – 2025) initiated the development of innovative, adaptable, and scalable nature-based solutions for urban water management. The core goal was to create a comprehensive process that promotes the adoption of nature-based solutions (NbS), reducing the discharge of untreated or inadequately treated polluted water into urban environments.

The project prioritized the development of modular, open-source tools that enable decision-makers to plan, design, and implement natural treatment systems effectively. These tools incorporate a holistic approach, considering environmental, economic, and societal factors, with a focus on life cycle analysis and circular economy principles.

To demonstrate the practical application of these concepts, the project piloted NbS for water management in seven countries: Belgium, Germany, France, Italy, Norway, Spain, and the United States. These pilot projects targeted various urban water streams, including raw wastewater, and pre-treated wasteawter, combined sewer overflow, stormwater, rainwater, and urban runoff. More information about the results of the project is available on the project website at www.multisource.eu, including pilot fact sheets, the NAT4WAT NbS technology selection tool, the MULTISOURCE Planning Platform, three policy briefs, and a multitude of open-access peer-reviewed journal articles. An open-access textbook on the fundamentals, process design, and implementation of treatment wetlands will be published and available for free download in early 2026 (Treatment Wetlands, Third Edition).