Sustainability can be defined as: “Development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (UN WCED 1987). Viewing water and sanitation through the spectacles of sustainability means to consider more than the pure technical aspects. Water and sanitation must also be connected to institutional, cultural and ecological aspects. This means that sustainable water or sanitary systems are not fixed to any one system, but essentially considers all available systems. In order to design or select a sustainable system for a given situation a holistic systems approach based on ecological thinking is important. This module will familiarise the student with the “Concept of Sustainability in Relation to Water and Sanitation” through lectures, texts, examples and exercises.