When you burn hydrogen you get one water molecule for every 2 hydrogen atoms, however, making hydrogen using electrolesis uses water.


The reaction to produce hydrogen via electrolysis is:

Water + Energy ==> Hydrogen(gas) + Oxygen(gas)

Where the energy used is electricity.


The reaction if you "burn" hydrogen, either in an internal combustion engine or fuel cell is the same reaction in reverse:

Hydrogen + Oxygen ==> Water + Energy

In the case of a fuel, the energy produced is in the form of electricity and heat.
In an Internal Combustion Engine, the energy produced is in the form of rotaional motion and heat.


So in the end burning hydrogen produces the same ammount of water that went into the production of that hydrogen.

Also one important thing to note is that hydrogen is not an energy source, it is an energy storage method. Gasoline can be pulled out of the ground and burned with relatively little energy consumption, whereas hydrogen is more like a battery. You have to use energy to charge the system and then you can later recover that energy. However, hydrogen has a couple of important advantages over batteries. While it is true that it is less efficient to store energy in the form of hydrogen and then recover it with either a fuel cell or an ICE than it is to do with batteries, hydrogen and it's associated storage container are much lighter than batteries. Also hydrogen can be refilled quickly, whereas it can take hours to recharge the batteries in an electric car. This means that a hydrogen car could be driven across the country with periodic short stops to refill the tanks whereas an electric car would require long stops. This means electric cars are more suited for around town use. The other important advantage of hydrogen is that you can modify an Internal Combustion Engine to run on hydrogen and gasoline, or a mix of the two. A supercharged pure hydrogen ICE can achieve the same power density as a comparitevely sized gasoline internal combustion engine. And hydrogen also has a larger combustion range than gasoline so it can be burned in a more lean mix, which leads to a higher efficiency.

Now on a different topic regarding crude oil availabilty, one thing to consider is that even if oil is produced in a continuous geological process and not by the decomposition of ancient sea life, the rate at which oil can be recovered from underground has reached a point where it is no longer possible to vastly increase annual oil production. So as the demand for oil increases, as it certainly will, due to the current industrialization in countries like China and India, it may soon reach a point that the demand for oil will overcome the ammount the can be pulled out of the ground and refined, regardless of how much oil is left underground. For instance, in the US, oil production peaked in 1970, and in Britain it peaked in 1999. China was an exporter of oil until the late 90's when they started importing oil. However, oil consumption is increasing which means a shortage will at some point occur.

Hydrogen by itself, is not an answer because it requires some other form of energy to be produced. To produce enough hydrogen to power the entire transportion sector in the US would require increasing the electrical production ability in the US to approximately twice its current level. But at the same time, since hydrogen could be produced when electrical demand was low, such as at night, it would not require doubling the current number of power plants. The existing plants could be operated at their highest power output all the time instead of just at peak load and the excess electricity could be used to produce hydrogen. With the addition of the new plants to produce enough electricity to produce hydrogen to power vehicles, the electrical supply grid would also become less vulnerable to massive power failures like the two major eastern US power failures.