The principles of water sustainability are not exclusive to one civilization without the other this make led the research problem to emerge as a question: "What is the methodology of water sustainability in Islamic architecture and how it can be used as a guide-line for achieving water sustainability in contemporary architecture?". To answer this question the research in its theoretical study demonstrated three points, begun with presenting the functions of water in Islamic architecture, then it explained how Islamic architecture depended on water as a design tool in the process of place making, and it ended with determining the principles and criteria of water sustainability in Islamic architecture. The research determined the methodology of achieving water sustainability in Islamic architecture. Depending on this methodology the research analyzed two case study projects: Alhambra palace in Spain and Al-Ghuri Sabil in Egypt, and then the research applied this methodology in one of contemporary housing projects in Egypt, and this led the research to emphasize its main hypothesis which state “the principles and criteria of water sustainability which preexists in Islamic architecture can be used as a guide-line for achieving water sustainability in contemporary architecture".