In most cases, you will need to change your water heater anode rod approximately once every 6 years so long as it operates under normal working conditions. However, depending on the composition of your water, you may need to change the anode rod more frequently.
For example, if you have soft water that has a great deal of salt in it, the water heater anode rod could corrode very quickly. In that case, it could deteriorate in as little as 6 months. Because of this, you should frequently and regularly check your anode rod to make sure that it is in good shape.