This volume was prepared by a collective of distinguished researchers and scientists from universities and research centers in Slovakia. The volume aims to provide useful tools to the scientists, practitioners, researchers, designers, and experts, although we hope that the students in the field of water management, water quality, water structures, and civil engineering will also find it of interest. We did our best to cover most of the essential topics concerning water resources in Slovakia with the needed depth to serve as a reference for graduates, scientists, practitioners, and experts of different organizations with responsibilities for water and landscape management. Sustainable development of water management is based on the principle that water as a natural resource may be utilized only to that extent which ensures future generations sufficient usable supplies of water in the seas, rivers, lakes, and reservoirs, and that reserves contained in porous environments below the surface of the land remain preserved in the same quantity and quality. It is evident that surface waters are more vulnerable than groundwater in terms of their hygienic quality and safety, but also of their protection as a natural ecosystem and maintenance of their amounts. For this reason, it is necessary to devote all the more attention to the protection of water sources. The first step toward adequate protection of water resources is to know their size and distribution and manage the extreme events in the period of climate variability.