You can't put in X amount of energy and get X+1. In a car you put in X amount of energy through burning fossil fuels to drive the engine, you then get X-1 in kinetic energy because of losses as heat etc...

The proposal for a water powered car is put in X energy to a "transformer" which converts the water to fuel, get out X-? then put that into the engine to get X-?? in kinetic energy (and heat loss).

Duh!