The Terrain Maker® system is unique in that water features have banks, and the water level is lower than the surrounding terrain. Streams and shores are made using ¼" hexes (TM2). If only 1 bank is used, it's a shore hex. Any number of flat water hexes can be used between the shores, to model anything from Antietam Creek to the Dnieper. Add a few white paint "waves" and make the bank a beach, and you can model an ocean for amphibious assaults. For most water, use a deep blue, like a new pair of demin jeans.

Use a pencil to lay out where the stream will be on the ¼" hex. Cut to two banks out with a hobby knife.
Pre-paint the pieces: blue in the stream bed and the sloping banks of the two parts cut out in step #1. Allow this paint to dry.
Glue the two bank pieces to the base ¼" hex. Finish the hex as shown above: edges painted green, top "grassed," and details added..... this. Bushes hug the shore, trees flourish by the moist streambed. A simple bridge and road complete the scene.
For beach hexes, just glue 1 side of the shore to the base hexagon. Each TM Tree kit includes detailed instructions for modeling these palm trees.