[readmodifywrite]

The issue there is desalinating the water in an environmentally responsible way. It's hugely energy intensive.

[symplee]

There have been some encouraging results recently. For example:

https://news.ycombinator.com/item?id=22269115

In any case, the time frame we're talking about is 10-20 years from now. Lots of time for even more breakthroughs.