For hydrogen production, water is for all practical purposes an unlimited source. To get a sense for that it's cute to use a unit of volume of 1 cubic kilomete

For hydrogen production, water is for all practical purposes an unlimited source. To get a sense for that it's cute to use a unit of volume of 1 cubic kilometer. The world consumes about 36 billion barrels of oil per year, which comes to about 5.7 cubic kilometers. As a very strange coincidence, we consume about 3800 billion cubic meters of natural gas; if we were to liquefy it, it would come to virtually the same volume like the oil, more precisely 5.9 cubic kilometers. All in all, let's say we consume about 10 cubic kilometers of fossil fuels in liquid form. Water contains about the same amount of hydrogen per unit volume as oil or LNG. So, let's say (in an absurd extreme) that all of the world's crude oil and natural gas use goes towards hydrogen production, and we need to replace that with water, and for some reason that water is gone after 1 use (it's not), then we need to use 10 cubic kilometers of water per year. The world oceans have about 1.3 billion cubic kilometers of water.