Urban stormwater, comprising rain and snowmelt induced runoff in urban areas, is recognised as a major transport vector of a wide range of contaminants to receiving waters. The contaminants transported by urban stormwater may cause adverse effects on aquatic organisms, thus contributing to the urban stream syndrome, defined as the ecological degradation of streams draining urban areas. Such adverse effects may also impact raw water sources used for drinking water production as well as marine environments in case of stormwater discharges in coastal areas.
Although it is established that stormwater mobilises diffuse pollution from a multitude of sources, the main aim of urban water management systems has traditionally been to protect urban areas from flooding by the direct discharge of stormwater to the nearest water body without prior treatment. Current development of practices for stormwater management has shifted to embrace technologies which address both stormwater quantity (flooding) and quality (pollution control) as part of an integrated approach to stormwater management. However, while treatment may improve the quality of the water being discharged to receiving waters, it may lead to other challenges such as moving contaminants to another media that needs to be managed at a later stage.
The sources of stormwater pollution
A major source of stormwater pollution is traffic and traffic infrastructure, which include, e.g., exhaust emissions, road and vehicle wear and road management activities such as de-icing and inti-skid practices. Contaminant groups mobilised by road runoff range from solids to organic and inorganic contaminants. Building and structural surface materials also represent major sources of stormwater pollution and may, depending on material type, release various substances to runoff. For instance, metallic materials, such as copper and galvanized surfaces, may release high levels of dissolved copper and zinc, with the dissolved fraction being more mobile and bioavailable. Roofing membranes based on e.g., bitumen or PVC may release organic substances such as alkylphenols and phthalates, while outdoor paints and renders may contain and release biocides.
Other important sources contributing to stormwater pollution include countless anthropogenic activities in urban areas: e.g., construction and industrial work; washing of road tunnels or buildings; the use of fertilisers and pesticides; littering and accidental spills. Atmospheric deposition, transporting contaminants generated in urban areas with subsequent deposition on drainage surfaces in wet or dry weather, may also substantially contribute to the pollutant load transported with stormwater.
Source control as the solution to stormwater pollution
Deciding when mitigative actions are necessary can be rather subjective and depend on, e.g., the ecological sensitivity of the receiving waters, the level of dilution between the pollution source and the receiving waters, and the pollutant concentrations or loads in the actual runoff. It may often be both easier and more effective to limit the releases of contaminants instead of applying treatment to the runoff. Thus, source control is often the most effective mitigative tool. This can be achieved by phasing out important sources, as in the historically successful removal of lead from gasoline, which dramatically reduced lead levels in highway runoff and other environmental compartments. Similar phase-outs could be achieved for problematic substances in building and structure surface materials, as well as in vehicle parts such as brake pads and tires.
The way forward – Challenges and needs
Source identification is a central part of source control, but remains costly and technically demanding, further complicated by insufficient product transparency and fragmented responsibilities among stakeholders, as well as a constant introduction of new products and materials on the market. The legacy of existing material stocks embedded in buildings and infrastructure continue to release pollutants for decades, underscoring the long-term nature of this issue. Addressing these challenges requires a fundamental shift in strategy, including designing products and materials with minimal environmental impact, implementing stricter chemical regulations, and promoting circular economy principles to reduce hazardous substances entering urban systems. This is an issue that intersects construction, manufacturing, transportation, and consumer behaviour. Effective solutions demand coordinated efforts among regulators, industry actors, researchers, and municipalities, to share data, harmonize standards, and develop innovative approaches. Without such collaboration, preventive measures risk being fragmented and ineffective.
A holistic approach should integrate stormwater considerations into urban planning, product design, and procurement policies, while establishing clear accountability across the value chain. Embedding these principles into governance frameworks will ensure that stormwater management evolves from reactive treatment to proactive prevention. By prioritising upstream interventions, encouraging cross-sector partnerships, and implementing structural changes, cities can move toward resilient and sustainable water management, not only protecting aquatic ecosystems but also contributing to broader environmental and public health goals and ensuring that urban development aligns with long-term sustainability.
Alexandra Müller
Associate Senior Lecturer in Urban Water Engineering
Luleå University of Technology
Sweden
alexandra.muller@ltu.se
Photo: Katarina Grankvist
