How we have created artificial rain for my short film - Overture.
Watch the film here: vimeo.com/37373013
Watch the 2nd featurette: vimeo.com/57389217
We have built the rain towers ourselves, basically from painting poles, garden hoses, sprayers, and a water pump which is connected to a portable water tank.
For long-shots, we've used our long rain tower, which is built from 10 sprayers. For medium-shots, we've used a double handheld poles with 2 water sprayers each, which can move with the characters.
For the shots where we couldn't physically reach the characters with the rain towers, we have shot and used a keyed rain footage which we added later in the post.
For this we have backlitted the rain and shot it over a black background. Then at the post we were able to key out the rain from the background. And guess what? We have decided to share the footage here with you freely. Use it in your wintery projects. A nice 'thank you' in the credits will be nice though!
The files are in their native h.264 full HD format.
In After Effects (etc), just change the blending mode to Screen or Add, and you're done. Notice that it will add some brightness to your shot, so just bright it down, and maybe even desaturate the blue tint it will may add.
(First music track by Kevin MacLeod, second by Dror Shiman)