I notice in another thread that many members are overlooking the water heater anode rod.

The anode rod should be checked at least once a year. Generally they last about two years.

The purpose of the anode rod is to provide sacrificial material for electrolysis that occurs between the metal parts of the heater and the hot water. If this anode rod did not exist or has deteriorated beyond its useful life the corrosion will eat away the tank itself.

The anode rod costs about $10 - $15 -- far cheaper than the tank.