Traditional tank water heaters last 8 to 12 years while tankless models can last 20 years or more. Factors affecting lifespan include water quality maintenance frequency and usage patterns. Hard water accelerates sediment buildup and corrosion shortening tank life. Annual flushing and anode rod replacement extend longevity. Signs of replacement include rusty water inconsistent heating leaks and age. Check the serial number to determine your water heater manufacturing date.