Comment by FredPret
If it's the same molecule but downhill and mixed in with some other ones, it's just x number of joules and y number of dollars' worth of infrastructure away from being among its own kind and uphill from your tap again.
We get blasted with an uncountable number of these joules from above (the sun) and below (nuclear). Our economy is generating an exponentially increasing number of dollars.
I understand wanting to be careful with resources, but not to the point where frugality becomes a goal in and of itself.
That's like saying fossil fuels don't actually pollute or emit greenhouse cases, because we're just X joules away from sequestering it back from the atmosphere.
Desalination, and pumping water over thousands of miles is extremely expensive. Sure, you're not wrong, but the values of X and Y are uneconomical.