It never fails, whenever fuel prices go up someone comes up with some new miracle that will reduce or eliminate your gas consumption. Back in the 1970s, it was 200mpg carburetors, magnets you put on the fuel lines and all manner of other things that never worked. One staple of these schemes has always been the car that runs on water. The latest example comes from Japan created by a company called Genepax. They have devised a system that consists of a fuel cell and a so called energy generator. The energy generator is claimed to consume water and breaks it down to hydrogen and oxygen which is fed to the fuel cell. While fuel cells are well understood and are known to work, the hydrogen generator is the issue.
Hydrogen can actually be separated from water quite easily with no energy input. Just put a piece of aluminum in into some water and hydrogen will be release as the surface of the aluminum oxidizes. The problem is that such processes are not sustainable. Once the surface of the aluminum is fully oxidized, the reaction stops. After this, the material needs to be reprocessed so it can be used again. This part requires significant energy input. Genepax has not revealed details of their process, however it is believed to be something along these lines. While the converted Reva electric car may indeed be able to run on water for a short time with no external inputs other than water, it's not clear how long that can actually happen. It may turn out that Genepax has come out with something revolutionary. More likely they are only showing part of the big picture right now and we aren't seeing the other part of the process that regenerates the energy generator.
[Source: Reuters, thanks to David for the tip]