You folks need to study the galvanic process. the rod is called a "Sacrificial anode", What does this mean:
If the water is of a type that tends to eat the lining of the tank for breakfast, The Anode sacrifices itself to prevent that from happening,, SOFT water is a great offender,, Or rather Softened, as most of the metals have been removed.
Heavily metal laden water.. Not so much.. Now, not all minerals are Metal, and those non-metal ones may deposit on the anode (And everything else) .
It is all confusing less you are a science major, and even then .. Well, you might wish to do a bit of extra studying.. I would if I did not have an Atwood water heater.
