First of all I want to show note I don't want to show just THE way to create a water map.
Water is one of the most difficult maps and you can't make one that you can use in all of your scenes, but for the best results you have to create one for every scene.

Daytime Oceans and water surfaces need much more work then a ocean at night, I've tryed to make a map that can be easilly modified so you can play on your own with the settings. I have also included a modified daytime image.

Step 1: First fire up the Modeler create a plane(here we take 2km*2km) and hit tab and subdivide the Polygones. Hit "q" and a surface.

Step 2: Now start Layout and put the obj. in it.

Step 3: go to Object "Properties->Geometry" and increase the "Display SubPatch Level" to 150 and the "Render SubPatch Level" to "300".

Next under "Deform" and add a Displacement Map and add the following settings:

Layout Type: Procedual
Layer Opacity: 7000%
Displacement Axis: Y

Procedual Type: turbulence
Texture Value: 3,155
Frequencies: 10
Contrast:12%
Small Power: 0,4

Scale: x/y/z 500m/500m/500m


Step 4: Now on to the map..open the "Surface Editor" and add a Texture in the Color slot.

Add 2 Gradients:



Now add a Bump texture map; here I added 3 layers:

Some basic settings:

diffuse: 100%

Specularity: 80%
Glossiney: 100%

Reflect: 0%

Bump: 100%

At last i added 2 shaders a "Fast Frensel" and a "Thin Film" if you make a daytime ozean you should add a "Real frensel"

Fast Frensel settings:

reflectivity: 70%
Specular: 60%

Thin Film settings:

Primary Wavelenght (nm): 441
Angle Variation (nm): 5

Color Mixing: Blend with 5%

At the end you have to add an enviroment, use SkyGen or Sky tracer or just add an image; in this scene I used SkyGen.

A little tip at the end: you can add a Null Obj. and put it as a reference object under the Texture Displacement to animate the water.

If you play a bit with the settings you can get some nice results. Check out mine:

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