Water painting is that form of the painting where an artist uses three things; brush, watercolors and canvas/paper. Usually, paints are made up of colors which are dissolved in a water-based solution. On the other side, the canvas/paper is often produced, completely or partially, with the help of cotton. This is to get a good texture and to minimize the distortion when the canvas/paper got wet.
The good artist usually uses hand-made canvas/paper instead of machinery produced material. Water painting is the too old form of painting. And there are a variety of water painting techniques such as painting wet-on-wet (both brush and paper are too wet), or wet-on-dry (wet brush on dry canvas/paper).
Although the paint dries quickly on the paper and you get a satisfactory effect but it is also something to be very careful about. The dried painting can be distorted if it gets in contact with water again. And hence once finished with the painting, it will need to be sealed with some protections like a waterproof spray, a plastic thin film, application of a transparent wax etc.