Plastic Wrap as a Technique
Here's a creatively, fun way to create water in a watercolor painting.
Paint a wet juicy swash of turquoise or blue green in an area on your paper where you would like to simulate water. While the paint is still wet, lay a piece of plastic wrap over top of the wet paint. Pinch and pull the plastic around.
Where the plastic is pressed down against the paper, the color will be the darkest.
You must leave the plastic wrap on the paper until the paint is dry. Once you set it down, do not lift it off of the paper. Simply work the shapes until you are satisfied you have some interesting shapes. If you try to create horizontal crevices, it will look more like water. You're manipulating the plastic almost like finger painting.
Leave the plastic wrap in place until the paint is dry. When dry, remove the plastic wrap and you will be left with a unique texture resembling shimmering water.