1. Open a picture inside Adobe Photoshop.
2. Press Ctrl+J to duplicate the layer and then change the blending mode to Multiply.
3. Go to Filter> Stylize> Find Edges and you should start seeing the watercolor Photoshop effect.
4. Now go to Filter> Noise> Median and play around with the settings to get the effect you like.
5. Here's the final result from this Watercolor Photoshop effect.