Generally in the US at least, on older houses it's just the water pipe, newer houses use a rod, very new houses use two rods because electrical code requires it

Generally in the US at least, on older houses it's just the water pipe, newer houses use a rod, very new houses use two rods because electrical code requires it now. Rods definitely do corrode and need to be replaced regularly. ~10 years for zinc coated steel and ~40 years for copper coated steel rods.