Water heaters are commonly called geysers (pronounced “geezers”) in India and South Africa. I’m guessing this is a result of these countries being former British colonies, but I don’t know if the same trend follows in the other Commonwealth countries. Americans just call it a water heater or a boiler AFAIK.
Edit: To clarify, I’m referring to the type of water heaters used to heat showers. Not kettles.
Edit 2: Apparently it is an old British term for water heaters. Full explanation of the word and its origins and multiple meanings in the comments.