it's a similar situation for food production. Theoretically we, as a planet, produce enough raw food products every year (calorifically speaking) to feed every person on the planet many times over. The problem is the fact that we can only produce the food and hence have a surplus within, the environmentally & topographically favourable areas where they are grown. This of course is no use to the starving billions around the globe every day who happen to live thousands of miles away from our surpluses.
Transportation becomes the issue...transportation cost money...money requires government / global backing which requires moral and political will power. Which all eventually requires that the 'haves' are forced to give something up for the 'have-nots'....which all results in a simple problem having an endlessly complex solution. We are after all slaves to human nature.
The same with water. As a few people have pointed out, we will eventually be forced to implement a national fresh water grid...it's the only logical way to readdress the distribution problem we face in the UK. I also agree with you, in that I feel that fresh, clean water and the ability to deliver it to where it is required, will become a much more valuable commodity over the next 100 years than say, crude oil.