The problem with Hydrogen, is that its not efficient (fuel cells apparently are only 40-60% efficient). In contrast, batteries are 90% or more efficient (and improving)

So, you'd be wasting 50% of the power generated, and wasting fresh water too… Thats all assuming too that the additional minerals in the water won't cause extra issues either.

Battery costs keep dropping, and the technology keeps improving rapidly.

If they can get the efficiency much higher, maybe… It also might make sense for long range cars (at the moment) due to energy density

But, in practice, companies like BP and traditional gas companies are the main ones who benefit from a hydrogen economy. Because they can use non-renewable to undercut everyone