In WaterGEMS or SewerGEMS for ArcGIS, when I move some parts of my network or vertexes of some pipes, the vertexes/nodes suddenly jump very far from the main drawing, with the adjacent pipe stretching far out.
This can be caused by using the wrong coordinate system with the wrong units. For example, if your model is in US units (pipe lengths in feet, etc.) then you'll need to be careful when assigning a spatial reference, when you first create the model. When assigning a state plane coordinate system, there are folders for both "NAD 1983" and "NAD 1983 (feet)". If you choose a coordinate system under "NAD 1983", then the units will not be correct and it can cause these problems. You will need to delete the geodatabase that you had created for the WaterGEMS or SewerGEMS model, start a new project, add existing project, create a new geodatabase and this time choose the correct coordinate system.
WaterGEMS for ArcGIS FAQ
SewerGEMS for ArcGIS FAQ