Water effects

[Cedar]

I've seen some really wonderful works by Lee, Moglet, Big Ron etc. who have some really great images that have a lot of water/rain effects added and I was wondering if someone can give me a general process of how that is done in Photoshop? i.e. what brushes are used, filters/edits made to darken, how the rain is made, stuff like that.

Thanks in advance,
Cedar