Trying to predict the numbers that will define the hydrogen economy are anybody's guess. And guess people will, because it leads to great headlines like, "Will Hydrogen Power Suck the Lakes Dry?" What are some of those numbers? The Hydrogen Association says that it would take 110 billion gallons of water a year to power all 230 million light duty vehicles in the U.S. using hydrogen fuel cells (although, to base your estimate on having all vehicles run on H2 is pretty bold). 110 billion gallons would be better than the 300 billion gallons of water it takes to make the gasoline that the U.S. uses in a year, but we're not sure if this number takes into account all of the incidental water that would be needed to make the hydrogen. (On a related note, does anyone have a good source for how much water it takes to mine lithium or make batteries?) For comparison, the U.S. uses about 4,800 billion gallons of water each year for "domestic personal water use." So, what's your guess?