Why do we need oil?

I seriously don't know why is oil necessary. I know oil is used to power up engines, but why is oil needed to make the engines work? Why can't they work with water or something else? Ive watched videos on youtube with people making car engines work with water. What else is oil used for? Can't we make... show more I seriously don't know why is oil necessary. I know oil is used to power up engines, but why is oil needed to make the engines work? Why can't they work with water or something else? Ive watched videos on youtube with people making car engines work with water. What else is oil used for? Can't we make engines or technology work without oil? What makes oil necessary for those technologies to work? I would appreciate if someone explain this to me in a simple way.
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