Anyone can print a digital image for display. Most printers will print on different types of paper including watercolour paper. Plus, digital cameras and digital art software make it possible to create art for printing. Getting a good print of a digital image is the tricky part. Images end up blurry, faded or messy depending on the printer setting and paper used.
Test Print on the Paper
When you first select your watercolour paper, test print on it with the printer's test print cycle. This ensures the printer's settings match with the computer's screen settings. It also shows you how colours are going to look on the paper and the amount of bleeding or "Dot Grain" you'll see with the ink on the paper. Water colour paper for printing comes with a coating of starch or gelatin called, "Sizing" to reduce the bleeding effect of ink through the cotton fibres.
Adjust Printer Settings
Another option to reduce dot grain is by adjusting the printer settings. For crisp, clear images, set the printer to the highest level dpi, or "dots per inch" which indicates how many dots of colour are placed per inch. Slide the individual colour values, cyan, magenta and yellow to a high negative number and increase the saturation just a bit. The numbering systems will vary from printer to printer, but with an Epson Inkjet the setting is plus 15 for saturation and negative 10 for the colour values. This provides maximum coverage without dumping a lot of ink on the paper.
Think About Paper Texture
Watercolour paper comes in many textures. Watercolour paper for artistic use is either rough, cold press or hot press. Rough is very stiff and has a lot of surface texture. It may even cause problems in the printer. Cold press is slightly bumpy. It's also very absorbent and might be prone to dot grain. Hot press is smooth and flat. It won't absorb the ink as readily so the image can end up a mess. The key is experimenting with papers to find a good balance. Some lower cost papers have grid marks or dots on them from the type of press used on the paper. It's up to you whether or not you find these marks distracting from the image.
Prepping the Paper
If using regular art paper you can prep it in a number of ways. Size the paper yourself before printing on it with a liquid gelatin purchased from the store. Conveniently, it's called "size" or "sizing." Squeeze a small amount of the liquid into a bowl. Brush it onto the paper with a wide, flat brush. Allow to dry. You can also consider experimenting with painting a clear gloss on the paper before printing. Applying a watercolour wash to the paper adds a coloured background for the ink image. Experiment with fully dried watercolour paper or slightly dampened with water. Avoid running wet paper through the printer for obvious reasons.