You might search for stock images of water drops on glass, such as here
. You'll probably have to buy an image to get a usable size.
You can put that on a separate layer above your image and experiment with blend modes. Hard light is worth a try. Color doesn't matter because you can clip a hue/sat layer to the drops image to control that.
It isn't real easy, but it can be done. Here's a quick and partial illustration of the kind of effect you could achieve (I have no idea what sort of image you're dealing with).