Valve added Flowmaps in the L4D2 and later versions of Source. Valve used Houdini to create theirs, but most people don’t have access or experience in Houdini to create flow maps in the fashion that Valve did.
What is a flowmap?
A flowmap is a 2d texture that, according to colour values: scrolls the water normalmap over it, creating the effect of water “flowing”, hence the name flowmap.
This guide will teach you how to author your own flowmaps for Source, I am using the Portal 2 branch, but Alien Swarm, and CS:GO will work too.