As JT said, photo-realistic water is tricky. You first have to decide what kind of water you want to depict. Shallow water needs more layers as you will have to show the bottom of the river (or pond) and then build up from there. Muddy or very deep water is easier as you wont need as many layers. Also as JT said layer masks are crucial to achieving good looking water. Check out the tutorial and try some different styles. I'd love to see what you come up with.