If the process of using hydrogen reactions with oxygen produces water vapor, you’re not “mucking” with water, but creating it.
But let's go with the notion that we are indeed creating excess water. Then the negative unforeseen complication just might be an over abundance of water. We see from weather systems what an overload of water can do to an area that receives too much too fast. As a result, it may start seeing landmass reductions, for all this new water must go somewhere. Will this creation of excess water causes these kinds of problems?
I'm just saying we never understand the consequences until we take that leap. But history has shown us that all innovations have both positive & negatives. We see the positives, which is what brought about the innovation to begin with, but we rarely if ever see the negatives in the development stage. We only see the negatives after implementation & expansion in usage of the innovation take place.
I engage in what's often referred to as playing the devil's advocate, probably do so because I am not an innovator. But I think it's something that we should examine fully, because there will be unknown consequences, because there always are with innovations. I hope that's really why I engage in it, to spark stimulating conversation. Perhaps I'm all wet as usual. I know it drives my wife crazy. 😋
Take the cell phone, a marvelous remarkable innovation that has allowed us to communicate to people around the world. The negative side that no one envisioned, is just how much it tends to isolate us from those in our immediate surroundings.