The best way to paint water is to paint on location. You need to study the wave structure. Waves start out larger and keep diminishing as they come ashore. I like to follow the shape of the wave and action with brush strokes moving the same way as the area you are painting.
I start painting with dark viridian green and cobalt blue as the under painting.
I then proceed with the color of the sky in the troughs of the waves. The sky is always reflecting onto the waves. I then follow up with the foam trails. These are painted with a light grey and then finishing up with stronger whites. To give more of an effect of splashing sometimes I use some controlled spattering of paint with a brush or old tooth brush rubbing your fingers across the bristles.
As the waves come onto the shore you will see some darkness in the sand where the wave has washed up. I use raw sienna and yellow ochre to achieve the color of the sand. To show distance across the horizon in water I use cerulean blue greyed down. Also you can grey down the cobalt blue in the deeper water. I like to use burn sienna for this. To show the dramatic light coming through the wave I lighten up the viridian green to get the effect I want. Water takes a ton of practice, although it is well worth it.
With time you can learn to even get the movement of the waves crashing down. Keep that brush wet!
Gary W. Odmark
HOW TO PAINT WATER