It looks like they use planar reflections for the water, like Half-Life 2.Well, GoW had plenty of reflective surfaces, not sure which tricks out of your lists were used, if at all:

Half-Life 2 - Screenshot 02 by Edveenn on DeviantArt

I found this document online, which seems to give a good summary of the available options, from page 18, and a table on page 24 with the advantages and disadvantages of each technique.
Edit: Anyway, the main benefit of ray tracing is it both reflects off screen objects, and works on curved surfaces.
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