Why do vehicles need gas to function?

For one, water is not combustable. In the early days of the auto steam powered cars weren't that uncommon. THey're a little dangerous by todays standards though. Imagine having a huge tank or boiling water/steam under compression and a burner underneath that with an open flame.

Look up the way an internal combustion engine works and that will answer your question in more depth.

If water would burn, this would be a good idea. (water can be split into hydrogen and oxygen and then the hydrogen can be burned, but this is not simple or cheap) Gasoline burns well, but any other number of flamible fluids would work with a little adaptation)

Didn't you know that if we put anything else in the tank, Bush and his buddies wouldn't be able to go golfing together any more? But on the real side of the question, water has been proven that it can do the job. I think the octane has something to do with the gas working, not sure, but I am sure that there are many other ways to operate a vehicle. One being the afore mentioned water. Then there is corn, electricity and some are saying even air is being tested. Hope I helped.

Water is not combustible. And car engines are combustion engines.

Water is not combustible. Gas, diesel, methanol, propane....are.

Water is not combustible. And car engines are combustion engines.