It's worth pointing out that hydrogen oxidizes in the atmosphere, unlike helium, so it won't escape as readily. Secondly, the Sun already splits water into hydr

It's worth pointing out that hydrogen oxidizes in the atmosphere, unlike helium, so it won't escape as readily. Secondly, the Sun already splits water into hydrogen and oxygen with UV at some low rate, and that has been going on for literally billions of years from now. I don't think this aspect of what you're talking about will matter before 200 million years from now or so when the Sun becomes intense enough to kick off runaway greenhouse effect (even without human effects) unless we produce so much hydrogen (and leak it) that waste heat of civilization becomes the limiting factor. There are other things to worry about.