One liter of water contains about fifteen cubic feet of hydrogen but a secondary energy source is required to release it via electrolysis. Stationary production facilities which can utilize green power (solar, wind, hydro-electric, etc.) as the power source for electrolysis are the most practical way to produce hydrogen from water.

The method is extremely simple. You could easily make hydrogen at home with stuff around the house (I've been doing it for some time). Collecting and storing it, however, are another matter.

Many ways to produce hydrogen remain undiscovered because hydrogen bonds so easily with other elements. There are thousands of simple compounds which contain hydrogen. We may find that some abundant naturally occuring compound will release its hydrogen when the proper catalyst is introduced, the chemical reaction providing whatever energy is needed.

There are also biological solution possibilities. It has been discovered that common pond algae will produce hydrogen when deprived of sunlight. Much research is going on to investigate this discovery.