Where does drinking water come from? For people living in parts of the world where fresh water is plentiful, it's not much of a mystery.

But for people living in the Middle East, parts of Africa, and other hot, dry places, the water situation is more complex. There, people depend on turning salty ocean water into fresh water--a process called desalination.

Now, water desalination is a life-saving technology; without it, many people simply wouldn't have access to fresh water. But desalination is also costly, especially to the environment. Here's how it works. Some desalination plants use high amounts of pressure to force water through membranes that remove the salt.

Other technologies involve boiling sea water and then condensing the salt-free steam that results. Both processes require huge amounts of energy, and so consume lots of fossil fuels, and emit tons and tons of carbo...
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