1. Water Occurrence and its Function in Natural Systems. Systems of the natural environment. Energy input as a cause of the hydrologic cycle. Hydrologic cycle system. interrelation of surface and groundwater runoff. Groundwater level regulation, soil moisture and soil structure formation. Climatological functions of water. Biogeochemical cycle system. Hydrologic cycle as regulator of biological processes. Runoff process as regulator of the living environment. 2. Water and its Function in Social Systems. Categories of water utilization. Water requirements and water consumption. In-stream and on-site water use. Municipal and rural water requirements. Industrial water supply and re-use systems. Water in agricultural systems. 3. Water Balance and Water Systems. Characteristics of surface and groundwater resources. Safe yield. Balance of water resources and needs. Minimum water table and minimum discharges. Active and passive water balance. Probability of the satisfaction of water requirements. Flow control and operating schedules. Systems in water resources management. Analysis and modelling of water resources systems. Economic optimization and financial analysis. Planning model based on physical parameters. 4. Impact of Development Activities on the Hydrologic Cycle. Changes in the hydrological data. Changes in the hydrological balance. Influence of forestry and agriculture. Influence of urbanization and industrialization. Changes in water quality. Environmental impacts of water development projects. 5. Water Development and Management Policy. Water management activities and organizations. Paradoxes of water resources development. Strategy of water resources development. Tactics of water management. Non-conventional techniques of water supply. Conclusions. References. Author Index. Subject Index.