Why does steam percolate from below New York city streets? (both)

Every time I see a scene of New York streets, there is always steam coming for the manholes.
Where does this steam come from?

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CheekyBadger · M

Steam is sold for heating purposes and piped around the city, these pipes sometimes have leaks and since to repair them requires the system be shut down they are typically left or a vertical pipe placed above them to vent,

Gusman · 61-69, M

@CheekyBadger So there is a steam plant somewhere running 24/7 boiling water?
Must be many miles of pipelines under New York City. 😲

CheekyBadger · M

@Gusman Yes - steam is often created for industry - e.g. food production, pharma, paper. Once it is created and used for primary purpose it can be used for other things like power generation or heating. The New York system is used for power generation. In UK I know of at least one power station that is fed by steam produced for chemical industry - the power station is contracted to produce the steam to run the industrial processes and they get it back to generate electricity as a byproduct.