ABSTRACT: The chapter examines selected ethical questions related to uncertainty, which affects most of our decisions and actions in the area of water resources management. After a brief discussion of environmental ethics categories, it discusses the essence of Integrated Water ResourcesManagement (IWRM) approach. IWRM is embedded in the context of sustainable development and thereby implies long-term management of water resources. The long-term aspects of IWRMare related to the issue of intergenerational equity. Difficulties in projecting uncertain future and possible needs of future generations are briefly discussed. The applicability of cost-benefit analysis and the related discounting are brought under review. Last part of the chapter is concerned with some ethical issues and uncertainty in transboundary water management. The fundamental ethical problem is how to induce countries to adopt a cooperative approach. The chapter makes the point that we will always have a degree of uncertainty no matter how much we increase our knowledge and we must learn to live with different categories of uncertainty in water resources management and make our decisions in view of these uncertainties.