Step 1. Open the Original Image
Launch Photoshop. Press Ctrl+O to open the source image to be modified. I used a photo taken in Venice by an inexpensive Canon camera.
Step 2. Adjust the Hue/Saturation
Lets improve saturation: Image > Adjustments> Hue/Saturation (Ctrl+U). This step is optional: you can skip it if your image doesnt require correction.
Step 3. Apply a Filter Forge Filter "Watercolor Painting"
Now we'll apply the Watercolor Painting filter. Launch the Filter Forge plugin (Filter > Filter Forge > Filter Forge).
Open the filter web page http://www.filterforge.com/filters/7227.html and click the 'Open in Filter Forge' button.
Note: if you don't have Filter Forge installed, download and install a free trial version using this link:
Step 4. Fine-Tuning the Filter Parameters
Now we've got the necessary filter and can figure out the parameters required for the modification. For the start let's try the factory presets (on the Presets tab) double-click a preset thumbnail. One of them is acceptable but can be fine-tuned. Click the Settings tab and start experimenting with the sliders.
One thing can be of great help: the 'Next variant' button in the Randomizer section. You can simply click it until you get sufficient results. The following variant seems to be close to perfect:
Step 5. Looking for Imperfections
Look thoroughly at the result. The dirty blotches near the boat reflection spoil the picture. Some extra correction is needed.
Step 6. Masking Places that Need Fixing
Undo the last action (Ctrl+Z) and start the color correction. Switch to the Quick Mask mode (Q) and use Soft Round brush to paint the areas that are meant to be preserved everything except the water.
Step 7. Fixing the Water with Masked Levels
Switch to the Standard Mode (Q) and invert the image: Select > Inverse (Ctrl+Shift+I). Go to Image>Adjustments>Levels and drag the slider until you get the detail that looks good to you.
Step 8. Sharpening the Water
For better results sharpen the water areas using the Sharpen Tool (R) with large diameter and soft edges.
Step 9. Final Filtering
Launch the Filter Forge plugin and apply the Watercolor Painting again. Here is the final result: