Inside every water heater is a long magnesium bar called an anode rod. The sacrificial metal protects the tank from rust by corroding first. Once the bar disintegrates, however, the tank begins to corrode. You can at least double the life of your heater by replacing the rod before it dissolves completely—every four years or so, depending on your water quality.
Start by shutting the cold-water supply line to the heater. Then turn off the gas line or circuit breaker. Attach a garden hose to the draincock and drain off several gallons of water. Be careful: The water is hot. Then remove the old rod by loosening its hexagonal fitting on top of the heater with a long-handled ratchet wrench and lifting the rod out.
Before installing the new rod, wrap its threads with Teflon tape for better sealing. Then insert the rod into the tank and tighten it with the wrench.
A final note: Bendable anode rods are available to fit into heaters with little headroom above tank.
