Pouring water into a car's fuel tank instead of gas would disable the engine. Gasoline is lighter than water, so it will rise to the top of the tank and float. The water, being heavier, would then become the first available substance to be pumped through the fuel lines. Water is not combustible and therefore it can't power an engine.
Will diesel fuel damage a gas engine?
Answered by Planet Green
Is using corn-based ethanol as fuel economical?
Answered by Discovery Channel
How does petroleum dependence impact our scarcity mind-set?
Answered by Steven Kotler of Abundance