I know this thread is archaic, but it's what I found in searching to get me going on getting realistic water effects.
The reason for my reply is to add one tidbit of information that will drastically reduce render times. In addition to defining a maximum altitude for the "wetness" layer, you should definitely set a minimum altitude to be at or slightly below the level of your body of water with a fuzzyness of 0. This will prevent the rendering engine from computing reflectivity for the surfaces under the water, which aren't actually reflective. I found this out by mistake when my 20 minute render turned into an hour and a half render when I added the wetness shader. Restricting the wetness to a minimum altitude as well dropped the render all the way back down to 21.5 minutes, but I get the proper effect where I need it.