[Confusion]

Clean water is not fundamentally a scarce resource. Almost nothing is. The only actually scarce resource, and the one everything depends on, is energy. Given enough energy, we can clean all the water we want and distribute it anywhere we want. Given enough energy, we could recycle everything down to the smallest granule of rare earth metals. We would only get into trouble once we would be using all of the stuff at the same time, but then, given enough energy, we could mine the moon, asteroids, other planets. Given enough energy, everyone would be warm and fed, without any ecological problems, because we could clean all waste and recycle everything.

In the end, it all comes down to energy. If some countries would spend even a fraction of their defense budgets on solar, water, wind or fusion power research, we would be there in a jiffy. We could have had more energy than we could ever use by now. Our progress is much slower than it could be, because energy is kept scarce.

[jonhendry]

Um, no. You might as well say that scarcity of energy is the only thing between us and free ponies for everyone.

Even if energy were free, there'd still be the question of paying for the facilities to purify the water. The kinds of places where clean water is scarce now tend not to have much money, or much clout, with which to get such facilities built. More likely you'd get wealthy people wasting vaster quantities of clean water, while the poor remained without clean water despite the theoretically easy availability of the required water purification equipment.

[Confusion]

  You might as well say that scarcity of energy is the only 
  thing between us and free ponies for everyone.

That's exactly what I'm saying, with the caveat that it will take time to get to the situation where everyone can turn the energy into free ponies. As you rightly point out, there is infrastructure required to make use of the free energy. However, if you would have free energy, that infrastructure will get much cheaper. The richer will sponsor infrastructure for the poorer, as has started happening more and more. We are slowly but surely succeeding in improving the living conditions of the poorest. The component cost of energy in everything is not to be underestimated. If you could eliminate that, things would drastically change.

The energy is there for the picking, but no country or company is trying hard enough. And why should they? What would they gain? That's the problem.