Question about hydrogen.

If hydrogen unleashes energy by combing with oxygen to form water, what happens to that water? Wouldn't busy cities have problems with that water from forming fog or from flooding if it is evaporated and rains somewhere down the road?

Current cars burning gas put out some water as a byproduct. That's a large part of the white smoke you may see coming out of exhaust pipes on humid, cool mornings. It's also a good reason to run your ar long enough to get the entire exhaust system nce and hot, in order to vaporize the water that condensed in there the last time to car was run. Otherwise it will rust out your exhaust prematurely.

So we're already dealing with this to some extent.

I don't know exactly how much water vapor an H2 burning engine would put out. But if it goes, say 20 miles for each gallon of water put out, that would seem to be spreading it pretty thin?

by splitting water into hydrogen and oxygen, it will recombine so that in total, no net gain/loss of water would exist.

It's hard to visualize the volume of the atmosphere, but it exceeds most people's imagination. It's very big, and it holds a lot of water.

More than 99% of the atmosphere is nitrogen and oxygen. Water vapor is the next most abundant gas, but averages considerably less than 1% of the total. Nonetheless, because total atmospheric volume is so large, this small percentage is equivalent to 3100 cubic miles of liquid water aloft as vapor at any one time. By comparison, all the water flowing in all the rivers of the world at any time is about 300 cubic miles. Remember that water expands to several hundred times its liquid volume when it turns into vapor. So the volume of water vapor in the atmosphere is several hundred times the liquid volume of all the rivers of the world. (These numbers have been rounded for illustration.)

A cubic mile contains 1.1 trillion gallons of water. A cubic mile is a LOT of liquid. The entire world goes through just about one cubic mile of oil in a year.

If everyone on the planet were to switch, and burn a hydrogen fuel of equivalent volume to oil, it would put roughly two cubic miles of water into the atmosphere each year. Compare that to the amount of water that enters the atmosphere by evaporation and by emission from plants: 280 cubic miles every *day*.

Even if the hydrogen fuel were less energy dense than oil, and we had to burn twice as much volume of it, the total yearly global water emission would be equivalent to about 50 minutes worth of natural evaporation and transpiration.

In short: don't sweat it.

Peace.