[Dylan16807]

But that sort of problem only comes up when you accelerate. If you maintain a frame of reference then you can handle things far more gracefully.

A shared reference frame over two points billions of light years apart can be established. You simply keep the distance between these points roughly constant, which holds the velocity of all points roughly constant, which keeps calculations of simultaneity roughly constant across the whole region.

I can then state that in the combined earth/reservoir plusorminus .01c reference frame that the water is already gone. And this is factually true. You still have to wait for information to propagate but everything works out. The timing has no disputes between any members subscribing to this reference frame.

Relativity doesn't cause major problems until you deal with matter moving at high relative speeds.

P.S. I'm deliberately ignoring the expansion of space in this argument.