The answer to 'what does water heater do' is that a water heater is a household appliance that heats and stores water for domestic use. It provides a ready supply of hot water for showers, laundry, dishwashing, and other household needs. Water heaters use either electricity, natural gas, or propane to heat the water, and they typically have a storage tank that keeps the water at a consistent temperature until it's needed.
Water heaters are an essential part of a home's plumbing and heating system, ensuring that hot water is available whenever it's needed. They come in a variety of sizes and types, depending on the size of the household and the specific needs of the homeowner.