Because water colours can not be changed (cf Corrections) they need to be planned in advance. Therefore, it is normal practice to begin by drawing the subject directly on to the paper using a 4B pencil, lightly, and avoiding any shading. Should you need to remove the pencil markings then use a kneadable putty rubber, applying a little pressure. Complex ornamental buildings and portraits will need a more elaborate drawing, rather than basic outlines for a simple landscape or seascape.