Sustainable urban drainage systems (SUDS) constitute an alternative to conventional sewer systems when managing stormwater in cities, wherein the growing presence of impervious surfaces is increasingly altering the natural hydrologic cycle. One of the main objectives of SUDS is to reduce the impact of urbanization on the amount of runoff generated by a rainfall event. In this context, this paper is aimed at showing the potential benefits of installing different types of SUDS in runoff management with respect to the common situation consisting of sewer networks. Moreover, the impact of these systems on runoff was studied at the spatial scale of an urban watershed using Geographic Information Systems (GIS), which are useful tools when both parameterizing catchment areas and locating suitable sites in which to install SUDS. Thus, a series of rainfall-runoff simulations were run in a real watershed located in the city of Donostia (Spain) using stormwater computer models, in order to compare the flow distributions produced by a design storm in various scenarios, with and without SUDS installed.