When it comes to warming up water for a hot shower, there are several synonyms for "water heater". One common term is "boiler", which refers to a device that heats water for central heating in a building. "Geyser" is another synonym, which is often used in the UK and India. "Hot water tank" is a popular term used in North America, while "immersion heater" is commonly used in the UK and Ireland. "Heat pump" can also be used to describe a device that heats water, and "tankless water heater" describes a type of water heater that heats water on demand without the need for a storage tank.