Previously I failed to mention that hardness has nothing to do with the anode rod being used up, or deteriorating.
Ion exchange water softeners work by attracting + charged ions in the water to the negative charged sites on the resin ‘beads’. The process is called ion exchange because the exchange is roughly two sodium, or potassium, ions for each ion removed. Ions removed are iron, calcium, magnesium, lead, copper, radium etc. and are much larger than the sodium or potassium ions the resin is regenerated with. The ions removed are soluable, meaning they are dissolved into the water. Softened water does not attack metals. Neither does sodium that is added in the process. Sodium or potassium comes from sodium and potassium chloride; water softener ‘salt’. The chloride part is not used and is flushed to drain. Chloride is corrosive to most metals; especially stainless steel.
Confusion exists due to softened water being confused with naturally soft water. Naturally soft water is water with little hardness but a lot of DO and CO2 content with little TDS and a low (acidic) pH. That water is aggressive and eats metals.
Other than stray elcetrical current, the biggest cause of anode rod deterioration is bacteria. The bacteria is primarily sulfate reducing bacteria (iron and manganese are others) and they thrive in low temp (<140f) water heaters and use the anode rod as a food source. In many cases this will ad a 'sulfur' odor to the hot water. Anod rods that are larger than normal with a softish fluffiness are under attack by bacteria. In most cases the water source will be a private well. City water that is properly chlorinated won't/shouldn't have bacteria of any kind in it. So maybe the tech wasn't diferentiating between the two sources of water. But if you have the opportunity, ask for the chemistry to prove his claim.
Here’s a goggle search for “sulfate reducing bacteria”, it provides very indepth information about it and the problems it causes. (copy and paste)
Here are two URLs that have a large amount of info on corrosion:
http://www.hghouston.com/TFAQ.html
At the bottom of this page, click on the click here to read what experts say about indices.
http//www.corrosion-doctors.org/NaturalWaters/Frames.htm
Gary
Quality Water Associates
