How can I convert my GIS data to a water or storm-sewer model inside ArcMap?
1) Follow the steps here for creating a new model for either WaterGEMS or SewerGEMS.
2) Use the steps here for creating a new model using the ModelBuilder tool to import the GIS data. Select ArcGIS geometric network or ArcGIS Geodatabase features as the data source type and select your geodatabase features to import. Then follow the subsequent steps in the wiki.
WaterGEMS for ArcGIS FAQs
SewerGEMS for ArcGIS FAQs