The original Arc Hydro has been redesigned to include a simplified framework for representing the basic surface water and groundwater features. Within this book we refer to the framework data model as the Arc Hydro Framework, or simply as the framework. You can add surface water and groundwater components to the Arc Hydro Framework to describe different aspects of hydrologic systems (the framework data model and the components are described in chapter 2). We refer to the groundwater components of the data model as Arc Hydro Groundwater, or simply as the groundwater data model, which is the focus of Arc Hydro Groundwater: GIS for Hydrogeology. Arc Hydro is not just a set of data models. Rich sets of tools have been developed to help ArcGIS users implement the data model, organize their data, and create GIS products. These tools make use of the standard data structures and the relationships between features within the data model to enhance the capabilities of ArcGIS for the management and analysis of water resources. For surface water analysis, a set of tools named Arc Hydro Tools has been developed by Esri.