If you're not very particular about the various detail issues, I suggest you take a normal texture and add the word SCROLL in front of it to make it scroll. If you do want all the spinky animation effects, you might want to try photoshopping the HL waterfall texture.
The waterfall itself is best made from func_conveyor. If you use a func_water, GOD WILL STRIKE YOU DOWN, and you can swim up the waterfall. Just be sure to align the texture in the direction of the conveyor. That way you'll get the full fun of being pushed down the waterfall instead of just falling.
If you want a detailed tutorial, you could ask the creator of the previous one. CrackerJack, if I remember right. He might have a back-up somewhere.