Corrosion within hot water heaters can be caused by water acidity, electrical conductivity, dissolved oxygen, and temperature. Water can react chemically with metal parts inside of the water heater. Acidic water can actually eat away at the metal. This corrosion process is accelerated with temperature. So as we heat the water for our usage, we actually can hurt the tank!
Anodes - The Staff of Life
Depending upon the source of the water supply, the dissolved mineral content can be high, medium, or low. Also, there will be different minerals present. The heating of water within a hot water heater and the motion of the water cause tiny electrical currents to be generated within the water heater. These electrical currents start to eat away at any exposed metal. That's why water heaters have anode rods as a part of their construction. These
anode rods are made of magnesium. The magnesium attracts the electrical current and corrodes more easily than the steel tank. However, if the anode rod completely dissolves, the electricity within the tank will begin to look for some other metal. That's why you need to check your anode rod periodically.
Many people know the difference between hard and soft water. Hard water is water that has a high amount of dissolved minerals. When hard water is heated, some of these minerals can precipitate out of the water and form a scale on the inside of the water heater. This scale can flake off and begin to collect on the bottom of the tank. This lowers the efficiency of the water heater by acting as a barrier to the flow of heat from the burner to the water. This scale can also corrode heating elements on electric hot water heaters in a very short period of time. Friends of mine have had to replace electric heating elements every 3 months because of this problem.
Electrolysis
Since we're talking about electricity, let's finish with
electrolysis. Iron is the primary metal used to construct hot water tanks. You can see this iron at the top of the tank where the hot and cold water pipes attach to your heater.
Often rookie plumbers or homeowners simply install a copper male adapter into the female iron tank fittings. This metal to metal contact of two dissimilar metals can lead to corrosion.
These connection points need to be isolated "electrically" from the water pipes. There are several different connectors made for this purpose. I, personally, choose to use di-electric unions. Good Luck!
Water Heater Anode Rods