A wet watercolour wash laid on a dry paper forms a shallow pool of colour which if left undisturbed, will form hard edges as it dries (cf Edges). By laying smaller, loose washes over previous dry ones, you can build up a fascinating network of fluid, broken lines that not only help to define form and suggest shapes but gives a lovely sparkling quality to your work. It is ideal for cumulus clouds and ripples on the water surface. A combination of hard and soft edges describes the subject more successfully and renders the picture more variety.
To avoid hard edges use wet-into-wet or a wash on dry paper, softened and drawn out at the edges, using the damp sponge, tissue or paintbrush.