Thoroughly clean the surface. If you are painting on an exterior, or outside, surface, you may choose to sandblast or power wash the wall. Alternatively, clean the surface with warm soapy water and a sponge---a technique that can be used for either interior or exterior surfaces.
Prepare the surface. If you are painting on brick, coat the surface with a masonry conditioner, available from hardware and specialty paint stores, before adding the base coat. Otherwise, simply use a surface-appropriate primer for the base coat.
Find an image of a wave to use as the reference image, or you may choose to paint one freehand. After the primer coat is completely dry, sketch the image onto the surface with charcoal or graphite.
Apply the darkest color first. Ideally, you will want to use two or three complimentary blue colors for the wave. Once the first coat is dry, apply additional layers, working from darker to lighter shades.
Add white foam details around the base of the wave and along the crest using a dry sponge. Pour a small amount of white paint in a paint tray and dab the sponge in the paint, squeezing any excess from the sponge. Create foam effects by swirling the sponge in small circles.
If your mural is on an exterior surface or in a high-traffic area, consider adding a finishing coat, such as a clear varnish that is water-based with a soft sheen.