ModelBuilder can be used to create hydraulic models from a variety of data sources such as GIS, data bases and spreadsheets (see Using ModelBuilder). Once the model is constructed, both the model and data source can be modified such that there are differences between the data source used for the initial model and data source at some later time. Manually tracking and resolving the changes in each can be difficult and error prone.

WaterCAD can create ModelBuilder snapshots when a model is created and use those snapshots at later times to identify locations where the original and current data source have diverged, providing the user with a way to reconcile those differences.

The figure below illustrates how snapshots are created and used:

1. At some time (1), the model is created or updated from the data source using ModelBuilder and the two are in sync. At this time, the user can create a snapshot (see Creating an Updated Model Using Snapshots) which contains the list of all data that has been imported from the data source.
2. At a later time (2-), the model and data source will have been modified. If the user wants to update the model, it is possible to import all data but because many users have made changes to the model that they want to preserve, users often preferred to import only that data that has changed since time 1. The user can select the snapshot from the data source from a given time and preview any changes (see Creating an Updated Model Using Snapshots).
3. In the preview, the user can review all instances where the original and current data source have diverged and select which data to place in the updated model at time 2+.
4. When the user builds the model (sync-in), only data that the user wants imported is used to update the model.

The above process provides the user with a way to better control data used to update the model.

Snapshots only save data for "domain" elements such as pipes, junctions, manholes and pumps but not "support" elements (Components) such as controls, pump curves, and patterns.

There is a separate snapshot for each element type (e.g. pipes, pumps). In the main ModelBuilder manager, the user must create a separate field mapping for each element type which can be saved I none connection or one for each element type.