The FUTURE of Vehicle Power: HYDROGEN

H2O is the output "exhaust" from the onboard Fuel Cell that generates the onboard electricity.  What a system!  It is here.
Germany has already launched the first Trains on September 16, 2018!  Hydrogen Fuel Cell Cars are also already here (see below).

The world’s first hydrogen fuel cell train rolled into the station. 

It was a world premiere being celebrated by 1) Alstom, one of Europe’s largest railway manufacturers, 2) the Minister of Economy and Transport of Lower Saxony, 3) the Federal Ministry of Transport and 4) the transport authorities of Landesnahverkehrsgesellschaft Niedersachsen (LNVG) and Eisenbahnen und Verkehrsbetriebe Elbe-Weser (EVB) in Bremervörde on Sunday 16 September.

The world’s first hydrogen fuel cell train rolled into the station. The Coradia iLint, built by Alstom in Salzgitter, Germany, is equipped with fuel cells which convert hydrogen and oxygen into electricity, thus eliminating pollutant emissions related to propulsion. 

source: https://www.energy.gov/sites/prod/files/2017/06/f34/fcto-h2-fc-overview-dla-worldwide-energy-conf-2017-satyapal.pdf