Worldwide, the phenomenon of hydrogen fuel cars is gaining currency. These cars produce zero-pollution, because the fuel i.e. hydrogen combines with oxygen to release the energy that propels the car. The by-product of this process is, of course, water, which surprisingly, is clean enough to drink.
On a lighter note, my use of hopefully in the above paragraph is considered incorrect by linguistic standards. But since this usage is so common, let me err.
(Report from the print edition of Times of India)