First, the mandatory pendantry. It's not a hot water heater, as it isn't heating hot water. It's a water heater, period.
To answer your question, it depends. Gas or electric (or oil)? How hard is your water? What is the pH? Do you flush the heater, and if so, how frequently? Is there a whole house filter, and if so, is it before or after the water heater?
Aggressive water will obviously shorten the life of a heater. Once the sacrificial anode of an electric unit is consumed, the rest will be eaten up in short order. Lack of flushing and lack of whole house filter will allow the buildup of sediment in the base, which acts as an insulator, particularly with gas or oil units, and the bottom of the tank gets burnt out. A quality unit (not something bought from a home supply store) should last 15 years, and possibly longer with diligent care.