On the initiative of His Excellency Emomali Rahmon, Leader of the Nation, Founder of Peace and National Unity, and President of the Republic of Tajikistan, the proposal to designate 2018-2028 as the “International Decade for Action: Water for Sustainable Development” was successfully adopted through a resolution of the United Nations. Over the past fifteen years, the initiatives of the Great Leader of the Nation concerning water and water policy have consistently received support through United Nations resolutions. It is well known to the international community that the leader of Tajikistan was the first to raise the issue of clean water from the United Nations podium before millions of people and world leaders. Following a resolution of the 54th Session of the United Nations General Assembly, 2003 was declared the International Year of Freshwater. Shortly thereafter, pursuant to another initiative of our great leader, His Excellency Emomali Rahmon, and in accordance with a resolution of the 55th Session of the United Nations General Assembly, the years 2005-2015 were proclaimed the “International Decade for Action: Water for Life.” Indeed, owing to world population growth and climate change, the shortage and unequal distribution of clean water have become increasingly acute and widely recognized. According to official statistics alone, every year approximately 4.5 million people worldwide die because of poor water quality and the lack of safe drinking water, while nearly 1.2 billion people suffer from various diseases. Water has transformed from an easily accessible natural resource into a critically important economic resource. The day when water may assume a role comparable to that of oil and natural gas, which today serve as instruments influencing global politics, may not be far away. It is now evident that water has become an integral component of both global and regional politics. In view of this, Tajikistan attaches great importance to its abundant water resources and regards their rational use and hydropower development as the foundation of the country's sustainable development. Ensuring effective water-resource management and transboundary cooperation is essential for regional stability and prosperity. Tajikistan is committed to constructive dialogue and cooperation with neighboring countries on the basis of the equitable and reasonable use of transboundary water resources. If the Nurek Reservoir cannot be protected from sedimentation, serious consequences may arise. Once the Rogun Hydropower Plant is fully operational and functions in coordination with other hydropower facilities such as Sangtuda-1 and Sangtuda-2, annual domestic electricity generation will reach 31-33 billion kilowatt-hours. This will not only make it possible to implement existing development plans and satisfy Tajikistan's own energy needs, but will also create favorable conditions for electricity exports to neighboring countries. At present, more than 300 hydropower plants operate on rivers of various sizes throughout the country. According to current plans, a series of large hydropower stations are expected to be built on the Panj River in the coming years. In particular, the construction of the Dashtijum Hydropower Plant, with an installed capacity exceeding 4 million kilowatts, will strengthen Tajikistan's energy position and create opportunities for the utilization of thousands of hectares of land in Khatlon Province and Afghanistan. At the same time, in order to preserve the country's water wealth under conditions of climate change, efforts must be made to protect these resources from depletion and pollution. This work, intended for Tajik-language readers, presents familiar but previously unsystematized characteristics and aspects from a new perspective. In addition to materials that were partially published earlier in various languages, it incorporates the latest scientific information and, most importantly, provides a comprehensive analytical synthesis of existing relevant materials. Taking into account the large amount of scattered information contained in domestic literature, the book places special emphasis on analysis and generalization, while also employing engaging illustrations that present familiar subjects from new perspectives and reveal previously unnoticed features. Overall, the book has a popular-science and reference character, while also containing a number of new scientific observations and viewpoints. For example, new materials are presented concerning the formation of Tajikistan's river systems, their overall chemical composition, and the total migration rates of elements. In addition, the book for the first time provides complete maps of the Syr Darya, Zeravshan River, Amu Darya basin, Karakul Lake basin, and the basins of rivers flowing to external drainage systems, thereby revealing new characteristics of Tajikistan's hydrological basins. In addition to hydrological maps, the book contains outstanding photographs of alpine lakes, glaciers, and other water sources in the country, taken by glaciologist and hydrometeorological expert Abdulrashid Tagoibekov of the Hydrometeorological Agency under the Committee for Environmental Protection of the Government of the Republic of Tajikistan. The authors express their sincere gratitude to him. The authors also thank editor Saifuddini B.Kh., proofreaders Machidov O.Sh. and Rakhmonova F., as well as digital cartographer Shamukhimov D., for their diligent work in preparing this book for publication.