Electric Elements
Galvanic corrosion is most common in electrical water heaters and appear on the electrical elements. The elements are the component that heats the water. Elements have a copper sheath and a steel base and if those specific parts become wet, electrolysis and corrosion may occur. An electrical element may be corroded enough to fail to heat the water. If you replace it and then in less than a year, the element may corrode again, then it is due to a faulty anode. Replacing the anode will prevent further element destruction. One way to prevent corrosion is to install galvanized unions with the plastic nipples on the top of the tank. Now you can thread galvanized pipe to the steel plumbing into the wall. Like galvanized plumbing, plastic plumbing will never have to deal with galvanic corrosion. PB and CPVC can adapt to most metal pipes.
Corrosion Caused By Softened Water
Softening water is the act of exchanging salt for hard minerals in water. Often the salt becomes more corrosive than the hard minerals. Softened water therefore consumes anode rods with greater ease. Anode rods inside softened tanks should be checked every two years, no more.
Anodes
Anode rods are very important to the heater's long-term health. Sometimes an anode rod develop a very hard covering of calcium carbonate on 100% of its surface. This layer prevents the anode from from stopping corrosion. The rod will look the same to the naked eye though. An anode that is covered in calcium carbonate will bend easily and that is the only way to tell.
Combustion Chambers
Combustion chambers in gas heaters have the potential to rust and corrode. To check the combustion chamber, first set the gas control to PILOT. Next remove the hatch cover. Now remove the draft diverter on top of the water heater along with the baffle. Using a flashlight, look inside the flue to make sure there is no water damage. If corrosion or rust appears, call a plumber for maintenance.
Rust and corrosion can occur inside a commercial heater as well. If you have the tank drained, check the inside for rusting. If there is rusting, call the manufacturer.
Solar Systems
Touching briefly on solar systems, it should be known that solar water heating has come a long way since its inception in the 1800's. Almost all corrosion problems have been eliminated. Solar systems sometimes use a heat exchanger. These machines have a special oily heat exchange fluid inside. The fluid does not drain in cold weather because it does not freeze either. Corrosion however may occur in this situation and may need to be monitored in the colder seasons.
Vent Pipes
If you have a gas water heater, your vent pipes could be subject to corrosion. Your vent pipes are the piping system above the water heater that helps the combustible gases coming from the water heater to escape to the outside of your house. Do not operate on the venting system yourself since plumbing codes are extremely specific and abundant when it comes to your venting system. Just make sure you can't see any rusted holes anywhere on your vent pipes or a unburned natural gas may escape through the holes. Call a plumber if you find this problem.
Corrosion Resistant Materials To The Rescue
If you're concerned with corrosion problems in the tank lining itself, many tank linings are created out of metals besides steel (which corrodes) and instead are made out of copper, stainless steel plastic, or cement. These materials are better than the usual steel and glass lining found on most water heaters manufactured still today. Ask manufacturers for tanks lined with materials other than glass and steel if at all possible.