Water is required for human endeavors as well as for the sustenance of the environment. Access thereto as well as, more broadly, the issues of the management of water resources are therefore growingly perceived worldwide as a new type of security issues, fundamental problems that human communities have to address capably in order to be resilient to the challenges they face. Reconciling different uses of water resources such as drinking water and sanitation, agriculture, food production, industry and energy, are major water security challenges in the Eastern European countries, as have already been and still are prominent concerns in their EU partners. Some international rivers shared by a few of the Eastern European partners of the EU, in particular, are already mentioned in international security documents produced by relevant international organizations as hotspots for likely difficulties in the organization of riverine communities and the international relations of the State involved. It seems undeniable that tensions and conflicts over access to water and its quality are likely to become more frequent and could endanger stability and security in the Eastern European region, as happens in other parts of the world. This could also have a direct bearing on the social and economic interests of these countries and their communities, as, more vastly, on the international peace and security in the region, including the EU. Climate change only intensifies the concern over the management of water resources in the coming times, as it adds to the seriousness of the matter. The whole Eastern Partnership has therefore been called to tackle these momentous challenges. A departing certitude is that the answers for such diverse issues involved in the concept of water security have themselves to be complex. They may only be found through comprehensive responses which take into account the close links with climate change, food security and energy, as they must bring together a range of actions and actors at different levels of governance. Through its EU Water Initiative, the European Union has been proposing that this calls for holistic, integrated water resource management, at national as well as transboundary level. A concrete objective of this water diplomacy undertaken by the EU in regard to the Eastern European partner states is the one of promoting collaborative and sustainable water management arrangements and to encourage and support regional and international cooperation in the context of agreed policies and programmes. In particular, the EU encourages the promotion of international agreements on water cooperation, like the relevant UNECE Convention on the Protection and Use of Transboundary Watercourses and International Lakes (1992) and the United Nations Convention on the Law of the Non-Navigational Uses of International Watercourses (1997) as important instruments to promote equitable, sustainable and integrated management of transboundary water resources in the region to be complemented by local basin agreements. For this policy of promotion and contractualisation of water cooperation, the EU predicates itself on the long tradition of cooperation and vast experience and knowledge of the management of transboundary waters in Europe. These proactive (international) partnerships are also to be replicated in very diverse social networks in the different countries themselves for ensuring the peaceful, sustainable and equitable access and management of internal water resources. The adaptation to so far-reaching and complex new methods of managing water resources is said to bear the reward of positive answers to the challenges of water security. However, more immediately they gave rise to a number of new legal instruments, both nationally and internationally, as well as new social partnerships and administrative practices that call for a comprehensive review.