How can I find out what version a model was created in?
The exact version number that a model was last saved in is identified inside the main model file. Locate the file for your particular product per the below list and open it (right click > open with) in a text editor like NotePad, NotePad ++, Wordpad, or another other simple text editing software. These files are simply .xml files, so you can open them in a text editor. On the third line of text, the build number will be shown after "ProductVersionLastModified=".
WaterCAD, WaterGEMS and HAMMER - .WTG file
StormCAD, SewerCAD, SewerGEMS, CivilStorm (V8i SELECTseries 3 and above) - .STSW file
StormCAD (V8 XM and V8i up to SELECTseries 2) - .STC file
SewerCAD (V8 XM and V8i up to SELECTseries 2) - .SWC file
SewerGEMS (V8 XM and V8i up to SELECTseries 2) - .SWG file
CivilStorm (V8 XM and V8i up to SELECTseries 2) - .CSD file
PondPack (V8i and above) - .PPC file
To locate the version that you need to download please see the instructions located in this wiki.