The problem of separating Water into Hydrogen and Oxygen through Electrolysis

 Though there is a lot of water on earth there is a finite or limited  amount. So, if you start separating hydrogen and oxygen through electrolysis and then use the hydrogen to power everything (like maybe in fuel cells) like astronauts use in space, eventually there is no more water left here on earth.

For me, this is the best argument against using water as a power source beyond hydroelectric generation in places like Hoover Dam in Nevada on the Colorado River or the Grand Coulee Dam on the Columbia River that my father and his two brothers helped build in the 1930s. So, there you are ONLY using gravity which is moving the water towards the ocean to generate power instead of separating the water PERMANENTLY into Hydrogen and Oxygen so it can NEVER be water ever again.