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Urban sprawl poses a persistent challenge for stormwater management, as low-density development patterns increase impervious surfaces while limiting the effectiveness and affordability of conventional, centralised drainage infrastructure. Nature-based Solutions (NbS) for urban areas, such as rain gardens, bioswales, and bioretention areas, have demonstrated strong potential to address stormwater quantity and quality challenges while delivering co-benefits such as urban cooling, biodiversity enhancement, and recreational value. However, despite extensive piloting, NbS for stormwater services are insufficiently mainstreamed in many urban regions and grey infrastructure often remain the default. A key barrier lies in the difficulty of developing scalable business models and governance arrangements that enable their long-term provision as part of regular stormwater services, particularly in dispersed urban environments.This paper examines how co-creation processes can inform the development of business models for mainstreaming decentralised NbS for stormwater management in urban sprawl. Empirical insights are drawn from structured co-creation processes conducted in the metropolitan cities of Lyon (France) and Milan (Italy), involving the metropolitan authorities responsible for stormwater management, water utilities, planners, and researchers. The co-creation activities aimed to identify priority planning units or contexts, relevant stakeholder groups, and feasible implementation arrangements for NbS by aligning technical performance requirements with regional policies and governance structures, financing mechanisms, and stakeholder roles.Across both case studies, three distinct urban environments emerged as particularly relevant for NbS-based stormwater service delivery in urban sprawl: (i) single household units, (ii) parking lots, and (iii) public parks. These environments differ substantially in terms of land ownership, regulatory context, investment logic, and operation and maintenance responsibilities, resulting in divergent requirements for viable business models. Rather than proposing a one-size-fits-all solution, the paper demonstrates how each urban environment is associated with a specific set of business model logics and governance pathways.For single household units, mainstreaming NbS depends on incentive-based and technical assistance models that minimise transaction costs for private property owners and enable aggregation at neighbourhood scale. Parking lots, typically characterised by mixed ownership, offer opportunities for public–private partnership models that integrate NbS into asset management and redevelopment cycles. Public parks provide a setting for utility- or municipality-led models in which NbS are embedded into existing public service provision and justified through multi-functional value creation.The findings highlight the importance of distinguishing between urban environments as planning and business model units when seeking to mainstream NbS in urban contexts. Co-creation proved instrumental in revealing institutional opportunities and constraints, aligning actor expectations, and identifying realistic pathways from pilot projects to standard practice. The paper concludes that successful mainstreaming of NbS for decentralised stormwater management requires environment-specific business models supported by coherent governance arrangements. Consistently, focusing on specific urban environments significantly reduces the complexity of navigating urban governance systems and can accelerate the development of scalable business models for NbS.