There's water, water, everywhere out there—literally an ocean's worth—but you can't drink it or irrigate with it for the salt. That used to be an insoluble technical and economic obstacle. But now, with snowpacks at zero percent and reservoirs looking more like puddles, engineers in San Diego are preparing to hook up a new $1 billion desalinization plant that will provide enough water for 300,000 thirsty people each day. 

First commercialized in the 1950s, desalinization has two main approaches: distillation (a variant on the process for making booze), which heats seawater and collects the salt-free vapor for recondensation into a liquid, and reverse osmosis, which pushes water at high pressure through membranes that leave clean water on one side and a concentrated brine on the other.

Today, 300 million people get some of their water from desalinization, according to the International Desalinization Association. Desal is big in arid nations like Saudi Arabia, Israel, and Australia, and on tropical islands that don't get much rainfall.