There was a recent episode of the Myth Busters TV show that tried this
approach. The basic idea was that you can use hydrogen as a fuel to run your
car. You can split water into hydrogen and oxgen using electricity. What
they found was that you can't make the hydrogen fast enough, but when they
stuck a hose from a tank of compressed hydrogen into the throat of the carb,
it did run until a there was a big backfire (obviously unregulated amounts
of hydrogen). The idea of water to run your car got a "Busted" rating.

-al sung
Rapid Realm Technology, Inc.
Hopkinton, MA