10.4122/1.1000001516 Zaizen, M. Matsumoto, Y. A Proposal of Combined Separate Sewer System (CSSS) DTU Library, Technical University of Denmark (DTU) 2005 Combined Separate Sewer System (CSSS) Sustainable Urban Drainage System CSOs Nonpoint Pollution Cost-Benefit Evaluation Takenaka Civil Engineering and Construction Co., Engineering Department en Conference full text 10.4122/1.1000001515 application/pdf 1 With respect to the systems of urban drainage, two main systems have been adopted so far, i.e., combined sewer system (CSS) and separate sewer system (SSS). Each of them has some merits and demerits respectively. Regarding the environmental demerits, the CSS has a problem of combined sewer overflow (CSO), and the SSS has a problem of diffuse pollution. Then, what system is more appropriate for urban areas? This paper describes a new concept of urban drainage system and important points to pay attention to while evaluating the system. The system, here named \342\200\234combined separate sewer system (CSSS),\342\200\235 is an essay on a new system of urban drainage when planning newly developed urban areas by means of making use of existing technologies. And the paper also searches for a possibility to adopt the CSSS to existing urban areas to improve the water environment.