BenderGuru’s Andrew Price demonstrates how to achieve a realistic render of a rain-saoked window, modeling the window and rain, then texturing and rendering the scene with depth of field.
Blender tutorial showing you how to make a rainy window
Andrew shows how to model the rain drop streaks, showing that you don’t always have to resort to a complex and overly thought out solution to create this type of realism in an image. Check out the tutorial for Creating and Rendering Rain on Glass using Blender here.