The International Water Research Alliance Saxony (IWAS) is addressing the global challenges concerning water quality in the areas of drinking water and sanitation, agricultural irrigation and the quality of surface and ground waters, as well as developing specific ecosystem-relevant services to be implemented on an exemplary basis in selected model regions. Locations (model regions) have been selected in Eastern Europe (R1), Central and Southeast Asia (R2 and R3), the Middle East (R4) and Latin America (R5) that are representative international regions with respect to climate, land use and demographic change (Ibisch et al., Helmholtz Centre for Environmental Research—UFZ, Department of Aquatic Ecosystem analysis and management, 2013). The causes of water problems and the relevant boundary conditions vary from region to region (Borchardt and Ibisch, Integrated water resources management in a changing world : lessons learnt and innovativeperspectives, pp 225, 2013). Mongolia and Vietnam were selected model regions in the first IWAS phase; the research was transferred and continued in one of the cross-cutting projects in IWAS II (Vietnam → capacity development) or in the frame of related project activities in Central Asia (R2 Mongolia, Karthe et al., Environ Earth Sci, doi:10.1007/s12665-014-3789-1, 2014). The IWAS consortium exists on scientific institutions like the Technische Universität Dresden and the Helmholtz Centre for Environmental Research—UFZ, Leipzig, as well as partners from industry like the Stadtentwässerung Dresden GmbH (SE-DD), DREBERIS—Dresden consulting for international strategies, and itwh—institute for technical-scientific Hydrology, Hanover. This thematic issue compiles the most important scientific results of the second phase of the IWAS project. The project itself and findings of the first phase were already introduced in a previous special issue by Kalbus et al. (Environ Earth Sci 65:1363–1366, 2012). Main results: The IWAS project is structured by the model regions (R) as well as by cross-cutting activities scenario analysis (Q1), technology development (Q2), governance (Q3) and capacity development (Q4).