is it possible to use water as fuel
According to the currently accepted laws of physics, there is no way to extract chemical energy from water alone. Water itself is highly stable--it was one of the classical elements and contains very strong chemical bonds. Its enthalpy of formation is negative (-68.3 kcal/mol or -285.8 kJ/mol), meaning that energy is required to break those stable bonds, to separate water into its elements, and there are no other compounds of hydrogen and oxygen with more negative enthalpies of formation, meaning that no energy can be released in this manner either.
Water-fuelled car