I consider that watercolour is the best colour medium for capturing short-lived moments. It is ideal for brief poses of the human figure but also for rapid painting of land- and seascapes where the light is continually changing.  For me it involves a delicate balance between controlling the water and collaborating with it. This lends a certain unpredictability to watercolour which keeps the paintings organic and gives them a life of their own. And occasionally when water, pigment and paper merge together in an alchemy which is unique for watercolour, then the artist can be content with his work.