Groundwater investigation needs professional knowledge about the groundwater occurrence and the dependent and independent variables. Reconnaissance survey is important to find out the possible groundwater potential areas, which is only possible with the help of groundwater indicators. This book discusses about the occurrence of groundwater and the groundwater indicators which are helpful to locate groundwater potential areas. This book is a directory to people who are working in the hydrogeology field and who wants to enter in this field. This book is a compilation of knowledge from different literature and experience which cannot be find from a single book. The chapters in this book confers about the importance of groundwater, groundwater sources, subsurface divisions of groundwater, groundwater occurrence, hydrogeological properties of rocks, aquifer & their types and different direct & indirect groundwater indicators. This book is written in a reader friendly manner with possible examples, preferable for students and the people who are working as a hydrogeologist and connected with the hydrogeology field.