All coatings used on steel tanks have imperfections and they get worse from rough handling, like during shipping. Once water finds its way through the imperfections to the steel wall, corrosion begins. To resist corrosion, lined steel tanks (not stainless or titanium) benefit from the addition of a sacrificial anode rod. The anode rod gives any copper in the system (from home piping) the chance to attack it instead of the steel lining. Only after the anode rod has disintegrated does the copper go to work on the steel tank through the imperfections. Most anode rods are made of magnesium—which, depending on the water quality, may give water an unpleasant odor. In these situations, aluminum is typically substituted.
Anode rods all have life spans that are dependent on local water quality. In some cases, even with hard water, lined steel tanks last for 25 years. (Albuquerque is one place—my solar storage tank is 24 years old.) In other locations, their life span can be 10 to 15 years. Anode rod replacement every five to 10 years extends the life of any lined steel tank—perhaps indefinitely if the rod is always replaced before the previous one is completely gone.