Dihydrogen Monoxide is so dangerous, that some rocket engines mix its base elements together in a combustion chamber, at a somewhat different mix ratio, at high temperatures to use it for fuel! And the exhaust left behind from those engines is 100% Dihydrogen Monoxide vapor!
Space Shuttle main engine:
[video=youtube;BK0nG9aY6qU]https://www.youtube.com/watch?v=BK0nG9aY6qU[/video]
Over 54% of the engines of the 3-stage Saturn-V used that same propellant!
OK hopefully mainly for the younger members of TRF who may not be up on some basics of real-world big rockets yet: Having fun with the fuel/oxidizer used for Liquid Hydrogen / Liquid Oxygen rocket engines (and their exhaust literally is steam, no pollutants). That is one the most efficient rocket fuel combinations that has been used for powering stages of a rocket. There are some even more efficient ones like Ion engines, but their thrust is so tiny that they are only useful on certain spacecraft once they are in orbit.
Also by now..... should be obvious but if not....
Dihydrogen Monoxide = H2O (molecule of two Hydrogen atoms and one Oxygen atom) = WATER
By a process of electrolysis, water literally can be separated into oxygen and hydrogen. Part of why water would be more valuable than gold in space (such as the moon or Mars) wth the right equipment. "Free propellant", as well as fresh breathable oxygen.