An annual inspection of the water heater's anode rod could prevent your water heater from leaking. All water heaters have a ceramic lining, but the last joint is not lined. An anode rod is put in the water heater as a sacrificial element. The impurities in the water will attack the anode rod before they attack and rust out the steel within the tank of the water heater.  Once the anode rod is dissolved, the next thing to rust out is the steel in the tank of the water heater. So replacing the anode rod before it is completely dissolved will greatly increase the life of your tank.  (Make sure to isolate the water heater before trying to remove the anode rod, instruction are in this site.)