It looks tricky, but it is actually just one waterfall twist on top of another, on top of another! 

So if you can twist two strands of hair I'm pretty sure you can do this, although it isn't quite that simple...

Here's a link to a tutorial, and yes I know that this picture and the one above look totally different but as soon as you get the concept down it will make sense how you create that (up there) out of this (below):