When you’re looking for a new water heater, keep in mind that the money you spend now may well be an investment that pays off in the long run.
In your water heater the anode rod plays a major role in corrosion protection. This protects your tank from corroding. Even though the tank is glass lined there is always imperfections in the lining. If it was perfect and seamless in ever aspect your water heater tank would never fail. For this reason the manufactures install anode rods. The anode rods in your water heater is a sacrificial rod that corrodes instead of your tank. The process is called electrolysis (the conduction of electricity through something melted or dissolved in order to induce decomposition of the melted or dissolved chemical or metal into its components.) This is the process that happens when you join two dissimilar metals, it creates a small electrical current. The less noble of the metals is the one that corrodes first. The dissolving chemical in this case is water. Water is a funny thing it dissolves almost anything but that is a different story for another day.
Anode rods are usually made of magnesium or aluminum with a steel wire at the core. Special aluminum / zinc sacrificial anodes or powered anodes may be used to resolve odor problems caused by bacteria in some water. Your anode rod in your water heater is usually the only difference in the warranty. The tank is the same for every water heater manufacturer that I know of whether a 6 or 12 year water heater. The difference in a 6 year warranty and a 12 year warranty is the addition of an extra anode rod. The manufactures are pretty good at figuring out the amount of time under average conditions how long that rod should last. So in some areas a water heater will last longer because of water quality is better as it pertains to hardness. The harder the water the more scale and other problems you can incur not to mention the amount of chlorine added to the water which is an oxidizer that will increase the corrosion process.
So we know all metals fall somewhere on the galvanic scale of reactivity. This is how they react when two metals are placed together in water, the nobler or less reactive one will remain intact while the more reactive one corrodes. When steel and copper are placed together, steel will be the one that corrodes. Indeed, steel is more likely to rust in the presence of copper than it would have been by itself. Magnesium and aluminum being a less noble metal than steel corrodes first so that’s why they are used as sacrificial anodes. This is the reason we use a dielectric nipple to connect a copper flex line on your water heater. You are connecting steel to copper and the dielectric nipple breaks the circuit which stops the corrosion process.
Starting to look at your water heater a little different? These anodes are replaceable and you can service a heater to last a very long time. It is just something I rarely see. Usually no one ask about preventative measures until their water heater starts spitting out brown water. By this time it is way to late the anode rod is gone and so is the tank on their heater.