Energy and water are largely fungible.

I don't think we can trivially turn (fresh) water into energy (yet?), so I wouldn't use that word. It's true that with enough energy, we can generally get some water purified (and distributed).

Fair enough, but if you aren't worried about energy you shouldn't be very worried about water.

The problem is that salt water is not available everywhere. Pumping water everywhere will be a problem.

A problem mostly solved by abundant energy.

There is at least a strong case for that, I agree.