Team-BHP - toyota eco friendly car

having seen the ad on the television a lot of times where they show that the car emits water molecules rather than the carbon exhaust fumes...
can someone explain wat kinda specifications the car has to be so eco friendly? and how it creates water molecules..what are the advantages and what are the disadvantages of the car and how is the overall performance of the vehicle..

I think you are talking about the Hydrogen fuel cell cars.I am not very sure .But here goes.....They do emit water as their only bi-product .This is done so by having a cylinder of compressed Hydrogen and Oxygen(or oxygen from the atmosphere...something like that) when you mix 2 hydrogen with 1 oxygen through a special membrane called PROTON EXCHANGE MEMBRANE ,the molecules split into protons and electrons .The protons are carried across the MEMBRANE to the positive electrode of the fuel cell thus generating the final product electricity and water (H20 = 2 hydrogen + 1 Oxygen).
The disadvantage i heard was the transportation of Compressed hydrogen.which can be dangerous and costly .Apart from that i believe that the overall efficiency is good.
Hope some senior members will explain this more sensibly