The method I use is pretty simple. It’s just an extension of the lasso-and-airbrush technique I use to render other objects. But here is a short demo in case it helps:
I start with flat colors. The water is on its own layer, so I can use it as a clipping mask for the next few layers so they don’t overlap anything else.
Next I use the lasso to draw in some highlights. You can study pictures of actual rippling water if you want it to look accurate, but I tend to just draw a loose web of rings.
Then brush in the lighter color with the airbrush. If you like, you can add another layer on top of this for extra highlights.
I like to add a layer of darker shapes underneath the first highlight layer for more depth.
Add details and finish.