I can't see how the hydrogen based energy production would actually mean more water vapour in the atmosphere, provided the hydrogen came from water in the first place. (McGrath)

(1) the cheapest way to produce hydrogen at the moment is not from water (but also from a nonrenewable source, namely natural gas).
(2) Even if all hydrogen would come from water in the first place, turning water into water vapour in the end increases the amount of greenhouse gas. We have loads of CO2 in the world. None of them worries us, except that small amount acting as a greenhouse gas. Water isn't problematic here, but water vapour could be.
(3) What makes water vapour less problematic than CO2 is that it eventually (and usually rather quickly) comes down. We call it rain. Therefore a human decision to stop adding water vapour to our atmosphere would have success within weeks. A decision to reduce CO2 (or other gases) would have success with a lag of decades. Water vapour, which actually is the largest contributor to the greenhouse effect, is therefore seen as less problematic.
(4) However, a grand scale water vapour addition to our atmosphere could have locally drastic climatic effects and globally perhaps too, for the amount of water vapour at any given time will increase, even if it all comes down fairly quickly. My guess is that high flying hydrogene powered planes will be the worst problem here.
(5) My point is not that this would not be an improvement, I actually guess it will be. I only want to warn against those thinking that everything will be unproblematic if only the oil profiteers will be replaced by environment loving people. Any energy production is dangerous and has some disadvantages.

I could find some articles, but I think this should make clearer my previous post.

Wolfgang