That's not the point.
The point is free energy, work, and thernodynamics.
If you begin with water as a fuel, and ends with water as a waste, there is no friggin' way any energy can be extracted for work.
Water can only be considered as a fuel if and only if you end up with a waste that is of lower energy than water. Unfortunately (as far as fueling is concerned), water is the lowest energy molecule you can make out of hydrogen and oxygen atoms, thus, water as a fuel is an impossible prospect.
Fusion creates energy, because 2 hydrogen atoms combine to make one helium atom, and helium is of lower energy than hydrogen, hence work can be extracted. The problem is that this process is spontaneous only at very high temperature, e.g. hydrogen bomb.