(references and tips to another card)
Forget black background, put some color and make water less transparent at the end, it should be more blue
Also, try to make a degradée, because water is denser at the bottom and receives less light, should be darker at the bottom.
The surface of water in real life is always reflecting a sky, blue or maybe cloudy. Use some sky environment to make it reflect more realistic.
Look at this cool solution, a spherical glass with the water inside, but you can feel the glass because of subtle reflections.
To the sand, try to use a texture representing the layers of terrain, should be better, as image on page 2 or 3. Or just change to some noise with sand colors and forget the texture, because in this scale, sand is too small, we shouldn’t see it.