An anode rod protects your water heater from corrosion by attracting the corrosive elements in the water, they will attack and "eat up" the anode rod rather than the inside of the water heater’s tank. These anode rods should be inspected and replaced annually. Atwood's anode rod is 4.5" long with a 1/2" pipe thread, while the Suburban anode rod is 9" long with a 3/4" pipe thread. These are easily replaced and should be checked every six months. Under normal use, the anode rod will deteriorate. It is recommended that it be replaced annually or when consumption of the rod is greater than 75%. 

This is an Atwood anode rod 4.5" long.

Note: Water with high levels of iron and/or sulfate will increase the rate of deterioration. To extend anode life, drain water from tank whenever the RV is not being used. Avoid any extended time of non-use with water in the tank.