Why are we in danger of running out of drinking water if desalinization technology is available?

To add to the anwsers above: dieing of thirst is not the real question. A lot of things use large amounts of water. Especially electric power plants that need huge amounts of cooling water, and many industrial plants, paper mills, etc. We might not die of thirst but we we surely might face some severe limits on our lifestyles and convenience. The price and availability of nearly everything will go up as water availability declines.