Sadly, there is such a thing as conservation of energy. That is an overriding principle that means that you can only ever get out what you put in so however you arrange to get the hydrogen out of the water you will have already expended that energy to do it.

That is why I regard hydrogen as more of a battery than a fuel.

The difference with what I call a fuel is that the energy was stored millions of years ago without directly costing us anything. We then find the coal, gas or oil and get the benefit without having to create it.