Watercolour paintings are seen as a good choice when it comes to buying original art, for those whose budgets do not stretch to oil paintings and if you are keen to purchase work by a particular artist.
They were originally used as a medium used for rapid sketches in preparation for an oil painting. Eventually they evolved into a very popular art form with artists and used to produce finished work, with a particular beauty in their unique crispness of line and sensitive, lucid transparent washes.
Created in the opposite way to oil paintings, working from light to dark, they use the colour of the paper as their light. Watercolour is also fairly flexible medium in that it can be applied opaquely or in watery washes that dry quickly.
In the past, watercolour paintings were seen as secondary examples of an artist's work and therefore more affordable, despite the skill needed to produce a successful watercolour. It is a challenging medium to master as an artist because of the element of fluidity, foresight and speed required.
Watercolour paintings like original drawings require more careful handling compared to oil paintings. Oils from your fingers will damage the paper and paint surface if touched too much.
The best protection for a watercolour painting is to be stored in a dark place with constant humidity (I guess why they are often kept behind curtains in art museums). But if you want to see and enjoy your watercolour whilst keeping it protected, you might want to hang it away from sunlight or source of humidity, in a UV protected glass frame with conservation grade acid free mount.