The overall goal of MULTISOURCE is to, together with local, national, and international stakeholders, demonstrate a variety of about Enhanced Natural Treatment Solutions (ENTS) treating a wide range of urban waters and to develop innovative tools, methods, and business models that support citywide planning and long-term operations and maintenance of nature-based solutions for water treatment, storage, and reuse in urban areas worldwide. MULTISOURCE will allow users to identify multiple sources for local water reuse, promote increased uptake of nature-based solutions, and minimize discharge of water that has not received adequate treatment. MULTISOURCE will deliver new knowledge about ENTS and their ability to remove waterborne contaminants and provide effective risk reduction for chemical and biological hazards, as well as their capacity to be integrated into the landscape and contribute to the improvement of urban habitats. The project includes seven pilots treating a wide range of urban waters. Two individual municipalities (Girona, Spain; Oslo, Norway), two metropolitan municipalities (Lyon, France; Milan, Italy), and international partners in Brazil, Vietnam, and the USA will contribute to each of the main project activities: ENTS pilots, risk assessment, business models, technology selection, and the MULTISOURCE Planning Platform. The use of urban archetypes in the Planning Platform will enable users to quickly classify regions (in both developed or developing countries) suitable for the application of nature-based solutions for water treatment (NBSWT) and compare scenarios both with and without NBSWT. This unique approach provides the knowledge, business models, and modular tools that will enable stakeholders to conduct fit-to-purpose, large-scale planning in their local region and, in doing so, promote circularity and sustainable development in the urban water sector and overcome barriers to widespread uptake of nature based solutions for water treatment.