The problem iss that it takes LOTS of both water and electricity to make enough hydrogen to be useful as a genset fuel. Both are usually in short supply on a bus. Even as an auto fuel, it is not a cost effective alternative, just a more enviromentally friendly alternative.
Not even 'environmentally friendly' strictly speaking (since more fuel is ultimately used), just 'lower emissions at point of use'. Same is true of electric cars, catalytic converters, and lots of other things we are told are 'envronmentally friendly'. If the electricity used was generated without the use of fossil fuels then there would be a net gain.
My Mum's hydrogen machine doesn't use much electrical power, but then it only needs to produce a relatively tiny amount of gas.
I heard a statistic once that said that more energy is typically used to build a car than that car will ever use during it's lifetime. I dont know if that is really true, but it sounds feasible when you consider everything involved in the mining, refining and transporting of the steel, aluminium, plastics etc involved as well as all the energy consumed by the car manufacturing plants and all their suppliers. If it is
true then the most 'environmentally friendly' thing we can all do is drive around in old, overbuilt, understressed, gas guzzling cars (and buses), and pass a law to force Ford, GM, Toyota and all the others to sack 95% of their staff and close down all their plants apart from their spare-parts divisions. Strange how I've never heard a politian propose that though.