is water4gas is effective why cant it is use by big players like toyota,gm etc?

[Anurag C]

recently i seen many review of water4gas technology many says they get 10% gain in mileage now i want to say that is this thing really works and if works why can't market players like car manufacturers like toyota etc that have engineering minds and infrastructure improve this technology and use in their models so the high fuel economy should be achieved -------