yes yes photomaster is correct. I think the way to implicate the water highlight texture is in another tutorial around here, methinks it has to do with script-fu->render->lava with horizons2 *winks*
animating it is a different story so many ways, wave/ripple/noise/blend/morph just to name a few, these examples are in no way the best you can do with gimp btw LOL the speed kept annoying me during playback..seems not realistic enough
and playing around with your image instead: