Yes It's a quick NPR
First I render my model with Twilight, I use only the water material and the glass material of twilght, And I setup a Spherical sky, shadow at 10. I don't edit any texture (no bump, no reflection.)
I use a gray scale image from SU, I choose multiply layer on gimp or photoshop and transparency at 25%.
I think that the image rendered and the shadow with Twilight even in small setting have a good quality.