Earlier quoted context omitted.
It takes energy, not time. It takes a long time if you passively wait for random environmental processes to slowly replace the water, and a very short amount of time if you actively apply energy to the problem.
That actually highlights the problem perfectly. Energy is the metric that matters. With current knowledge and level of technology humanity has, we can make almost anything by applying energy to shuffling dirt. Need gasoline? We can synthesize it. Need gold? We can recycle it out of stuff. Need drinking water? We can make it out of almost anything. All that's needed is energy, which is something we don't have much of…
Why not run the world on nuclear power? With breeder reactors, there is enough uranium for more than million years of current world electricity consumption. Nuclear energy is cheap, and modern reactor designs are safe.