There seems to be a powerful element of pessimism over the concept of drinking water. It seems like nobody has any ideas how to fix this. So let me ask you this: Where does Saudi Arabia get its drinking water? The answer is desalination.
Here's an article about using wavepower to generate electricity. The idea is that these systems could sit off the coast of California and deliver power to the grid. But I ask why deliver power when there is such a crushing need for water? How about attaching a desalination plant to the wave power plant and pumping millions of gallons of fresh drinking water to the parched land of California?
Or how about this: let's move all those melting icebergs into desert and dry areas which desperately need water. How will we move them you ask? How about a new fleet of airships to transport icebergs to deserts.
Finally, let's just make water out of thin air. Even in a desert water will condense from air onto a plate chilled to a temperature below the dew point. Connect a solar panel to a thermoelectric cooler and you get water.
None of these are free, and it appears the problem with water is that everybody wants free water. We are moving into a water where water is not free. But there are many ways to give water to thirsty world. All it takes is a little imagination.