The life expectancy of a water heater is approximately 15 years. To find out how old your water heater is look at the serial number. The first four numbers of the serial number are the month and year. If your water heater is not yet 15 but is not working, leaking, making noises such as banging or whining, or is rusty call Putman & Son’s Plumbing right away to fix or replace and avoid further problems.