Water balance studies for large and small river basins are the subject of this book. Here, the specific focus is on the soil and water assessment tools (SWAT) model coupled with geographic information system (GIS) remote sensing data for a comprehensive study. Some books available in the market provide an overview of different hydrological models for water balance but not specifically for the SWAT model. This book effectively utilizes the SWAT model to study the water balances in small and large catchments with consistent competence and excellent accuracy for yearly and monthly water balance modules along with suspended sediment yield over several slope classes of the catchments. The approach is new and has been successfully utilized, as discussed in a case study on the Taleghan Catchment in Iran. These implementation models may assist as advantageous techniques for incorporated management of catchments in the direction of sustainable development. This book will help readers who wish to study all the changes related to those in water balances.