No, it's entirely abstract. Nothing in physics depends on what you identify as "the original body of water". When you take a drop of water and add it to the original body of water, the best, most accurate story of what happens according to physics depends on where every particle of water is at each time, with the tie coordinate and the spacial coordinates chosen arbitrarily and coordinated with other arbitrary choices according to general relativity. Even if we just stick to special relativity the "instant" is different for different choices of time coordinates. Since "instant" has spacial properties, it cannot be something that ignores relevant dimensions. We know that simultaneity has spacial properties because we aren't merely concerned with what is simultaneous at the same place, we are concerned with what we can take to be simultaneous at different locations. The lesson of physics seems to be that we have arbitrary choices over what we take to be simultaneous at a distance. Until you can present a theory of gravity that does as well as general relativity in describing gravity and has an absolute definition of simultaneity, I will be forced to reject your simple, vague, and aphysical idea of simultaneity.