Painting water is one of the most technically complex challenges in digital painting because water has no fixed appearance — it's always a reflection or refraction of something else.

The framework that organized my thinking: still water is a mirror. Moving water is a distorted mirror. Deep water adds the color of the water itself (absorption and scattering) to the mirror. Breaking water adds foam and air bubble patterns.

For still water: paint what's above it, flip vertically, shift toward the water's color slightly (desaturate and blue-shift), add a subtle horizontal softening.

For moving water: the same flipped reflection, but with horizontal distortion that follows the ripple direction and increases with wave height.

For ocean water at distance: the surface color depends on the sky angle and viewer angle (Fresnel effect). At grazing angles you see sky reflection. Looking more directly down you see the water depth color.

The most common mistake I see: painting water as a flat blue surface. Water has almost no inherent color visible from above. What you're painting is almost always the sky or the shallow floor showing through.