Jump right in with the Brush tool and get creative with this watercolour painting technique
Begin by creating a new layer. Draw out the simple shape of the water with a round brush. Get a good feel for the shape of the water. When finished, reduce the layer’s Opacity to 50%.
Set the brush’s diameter to a small size. Press Cmd/Ctrl+Shift+N to create a new layer. Using the rough sketch as a guide, sketch out more detailed water with lots of sketchy lines to illustrate the direction and flow. Hide the rough sketch guide when it’s no longer needed.
Add detail to the background using the same technique. Make a new layer and then sketch some waves in the distance begind the main waves we’ve already drawn. Reduce this background sketch layer’s Opacity to 50% to give the impression that they are farther away.
Change both the foreground and background sketch layers to Multiply mode. This will keep the sketch visible throughout the colouring process. We will also Lock Transparent Pixels on these two layers by selecting the layers individually and pressing the / key.
Make a new layer underneath the sketch layers and set the mode to Multiply. Using a watercolour brush, paint in blue waves without lifting the brush to get a thin coat that covers the entire foreground, except for the wave peaks. These should remain colourless.
Press Cmd/Ctrl+J to duplicate the watercolour layer, then press Cmd/Ctrl+E to merge the two layers into one. Next, use the Brush tool to paint in lines flowing in the direction of the waves and underneath the curve of the big wave.
Grab a lighter shade of blue and paint in the base coat for the background waves, then follow it up with a few brushstrokes under the wave curls ad along the water flow. We’ve also used a grey-blue colour on the foamy peaks.
Cmd/Ctrl+Shift+J and make sure this new layer is underneath the sketch but above the colour in the stack. With a white colour, paint in short dotted strokes as spume and foam. Strokes along the curvature of the water create the impression of highlights.