Your water object could have a complex surface, and you could animate it by pulling points up and down. Another way is to use a texture map, made in photoshop or paint program - gray scale, with rings - could take some work but you could make 5 - 10 frames and loop to make an AVI or QT movie, like white rings on a black background - make the rings grow and shrink or dissapear/ move. Loop it. You could also try potentilizer ( a plugin). Post what you come up with.

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