"Corrosion" refers to the degradation of a material, such as those used in home plumbing, by chemical reactions.
Metals used in home plumbing possess a unique combination of strength, durability, corrosion resistance and low cost. In most cases, these characteristics have been established by decades of experience; materials that fail are discontinued.
When immersed in water, all commercially available metal pipe materials will corrode. In the vast majority of cases, however, corrosion proceeds very slowly, and it is not a significant concern.
The two main consequences of corrosion that might concern homeowners include:
Use of plastic pipe may eliminate certain corrosion problems; however, other problems have been associated with plastic. For example, under some circumstances bacteria can grow more rapidly on plastic pipe surfaces than on copper pipe. While not all these bacteria are harmful, production of safe drinking water requires elimination and control of bacterial growth at every reasonable opportunity. Certain chemicals can also migrate into drinking water through plastic pipe. In addition, because plastic is non-conductive to heat and electricity, plastic pipes might be more prone to bursting in very cold weather and cannot be used to ground electrical appliances.
This is not meant to discourage use of plastic piping, which has its own merits, but to demonstrate that there is no perfect plumbing material that could be economically used in all situations.
On a copper pipe, corrosion usually eats away at the surface slowly and uniformly; as a result, copper pipe normally lasts hundreds of years without problems. "Pitting" occurs when excessive corrosion occurs at a small area on the pipe surface, causing the pipe to fail prematurely.
There are many theories about how the process is initiated, including improper installation, bacteria, electrical grounding, pipe manufacture, water quality, or a combination of these and other factors.
The most important thing to do is replace the failed pipe section to limit water damage. In some outbreaks of pitting corrosion elsewhere in the United States, homeowners experienced leaks about once a week, and felt compelled to turn off their water service whenever they left home. Thankfully, this frequency of pitting corrosion is not observed in the WSSC system.
Dr. Marc Edwards of Virginia Tech, a nationally-known expert on copper corrosion, did extensive studies for WSSC. As noted below, he recommended that WSSC begin adding orthophosphate to the water. Dr. Edwards has also suggested that installation of a class II activated carbon filter (this removes 50 – 75% of the chlorine) at the point-of-entry into a house may reduce incidence of copper pitting in systems like WSSC's. (It is not recommended to use filters that remove all of the chlorine.) The plastic filter housings and the filters themselves, which are 10" long and rated for 1-5 um particle removal and Class II chlorine removal are available at hardware and home improvement stores. The filter element must be replaced when the flow rate gets too low, or every 3-6 months, as per manufacturers’ instructions.
No. There are many cases in WSSC’s service area where a homeowner experienced a single leak from pitting corrosion, replaced the affected pipe section, and the problem never recurred. On the other hand, if you have had one pitting failure, you are statistically more likely to have another.
No. Inexplicably, two adjacent houses can be constructed at about the same time, with pipes from the same manufacturer and installed by the same plumber, and one may develop a serious pitting problem while the other does not.
Replacing all your pipes with new copper pipes may result in an extended period without pinhole leaks, but there is no guarantee. A few WSSC customers have reported that new leaks have occurred in replacement copper pipes. Your own decision to replace plumbing should weigh the costs for your particular situation versus these possible benefits.
As recommended by Dr. Edwards after extensive research on the WSSC situation, we began adding orthophosphate to the water in late 2003. Through 2003, about 5,200 WSSC customers had reported leaks to our database; the rate has steadily declined with about 200 reports in 2004 to only six in 2010.
We encourage you to consult with a licensed plumber(s) prior to performing any major work on your home plumbing system. Additionally, as with any major repair and business transaction, it is generally beneficial to solicit more than one estimate for the work.
The following web sites provide product information about two WSSC-accepted plumbing materials for above grade water distribution - copper tube and Chlorinated Polyvinyl Chloride (CPVC):