Another way to make it rain. Find a nice picture of water drops. Neutralize it and add it to a new layer over your image.
Save this file as a PSD. call it Drops (or whatever).
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Then turn off the water layer and click on the background image.
Now go to Filter/Distort/Displace
Apply these settings.
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Click OK and select the PSD that you just saved (Drops)
It should look like this.
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Now activate the water layer and set it to soft light, or overlay.
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There ya go.
