Fuel from water is the holy grail and it fascinates me. I'd love to ride on fuel
from the tap but wont be parting with any cash until I'm fully convinced
The problem here is physics, it takes more energy to break the H2O bond then you'll get out of it in return as a fuel.
LPG is nice but the carb system is very tricky.
CNG/LNG is ideal but is even more difficult to deal with. We actually have some CNG stations now and a lot of vehicles in town that run off of it, it's selling for a bit over $1 a gallon. As with LPG, it really requires a much higher compression engine to get the full benefit from
When I lived in Texas some of the school districts converted Diesel buses to run on propane. The higher compression of the diesel engine gives satisfactory performance from the propane.