I think that localization and distribution of these types of processes like making water drinkable is going to become a huge trend, just because it makes a lot of sense.
For one thing, its easier to scale out in smaller chunks. Its also more robust to have lots of small production going on than to centralize. And technology tends to miniaturize.
I think that there may be other small but incredibly capable devices for producing things like food and goods. This leads to less reliance on more centralized traditional 'economic' distribution systems and greater security for local groups and individuals.
There does seem to be a trend toward more distributed and self-reliant production being enabled by improving technology: 3d printing, aquaponic gardening, biofuels, etc.
Still, the lower-level components and building blocks of the technologies that enable these applications still needs to be designed and distributed, and even those who generate their own electricity, grow their own food, and purify their own water are going to find it challenging to manufacture their own solar panels, construct their own pump systems, etc. More and more hackers might be designing homebrew electronics, but we're still a long way from DIY silicon fabrication.
So it's not that the large-scale, centralized economy will go away; it's that as the value of economies of scale in production of consumption goods diminishes, the centralized production systems and complex distribution networks of the industrial economy will pivot, and end up supplying tools and raw materials more, and finished goods less.
I bet over the next century, we'll see a gradual reversal of the economic patterns of the last 150 years or so, with more and more people adopting a kind of high-tech homesteading, fewer people working as employees for others, and finished goods being increasingly produced by end-users themselves or by smaller cottage industries, with the industrial infrastructure increasingly supplying inputs rather than final products.
For one thing, its easier to scale out in smaller chunks. Its also more robust to have lots of small production going on than to centralize. And technology tends to miniaturize.
I think that there may be other small but incredibly capable devices for producing things like food and goods. This leads to less reliance on more centralized traditional 'economic' distribution systems and greater security for local groups and individuals.