Carbon Steel in Potable Water System | Eng-Tips

Hello,

Is it acceptable to use carbon steel pipe in a potable water system?

I am currently upgrading a fire protection system at a complex with approximately 5 buildings. There is one fire pump that services all the buildings and the pump was added a few years after the buildings were constructed. The water main was cut into and the fire pump was installed. The system is set up so water flows from the water main through the fire pump system, then back to the main and on to the complex. During normal operations all the treated water from the town source flows through the pump bypass. This means that all the fire water and potable water for the buildings run through the bypass. This bypass piping along with the rest of the fire system piping is made from carbon steel. The water main from the town is made of ductile iron.

I had contractor look at the fire pump regarding some upgrades to the system and he advised me that the carbon steel piping is not allowed by the National Plumbing Code of Canada. Is that correct? Should the existing carbon steel pipe be replaced? If so, what are acceptable materials?

Thank you
I am not familiar with all potentially applicable Canadian codes for dual systems inside and outside of buildings etc.; however, I have noticed a sort of history/overview of many different types of pipe used for potable water distribution, including decades of steel pipe use in the USA per Figure 1 on page 3 and Table 2 on page 5 of the U.S. Environmental Protection Agency document at With regard to the latter question however regarding suitability for potable water/water quality, it appears that likely a great deal of unlined and galvanized steel pipe has been used for potable water service in the past and as noted in the aforementioned reference (and I suspect likely still used in many areas of the world, including the USA); however, see per Figure 1 of the aforementioned reference that after the 's there was more common promotion/use of cement mortar linings for at least the type of distribution piping included in this history. This is not by accident as cement mortar linings can at least in some aggressive water conditions be important to minimize internal corrosion and maintain flow properties over time.
Most states in the USA now require that all new materials/pipes/linings/coatings etc. in contact with potable water have ANSI/NSF 61 listing as suitable for that service. While perhaps you could check to see if your sort of piping had/has any similar/comparable listing, I guess the lack of a listing would of course not necessarily mean that there would be a problem with any sort of existing pipe. You might therefore want to at least check current ANSI/NSF 61 (or other applicable standards) pipe and lining vendor certification/lists for pipes that look like yours, with your local water provider for more information experience with such pipes and their specific water analyses, and/or actually have the water coming out of the taps tested. I guess some water might go bad in any pipe material after a given period of time, depending on what one does or doesn't do to it!
I think for many reasons, including the standard availability of suitable/proven cement mortar linings, buried piping for dual service (potable water and fire protection) in the USA in say the most commonly used sizes of 6” (~150mm) through 16” (~400mm) is more likely to be cement mortar lined ductile iron pipe than any sort of steel (see percentage entries in Table 2 etc.) On the other hand, there is some significant use of cement mortar lined steel pipe in some areas for very large diameter water transmission. I think AWWA Manual M11 for steel water pipes (depicting now 6”-144” sizes in some tables) now mentions various types of linings/coatings for steel pipe, and further says that “linings must meet toxicological requirements for potable water”. However, it also gives readers an additional statement that cement mortar linings “have provided many years of excellent service”.
I would think piping inside buildings, including perhaps some smaller sizes of plumbing etc., could conceivably involve some different considerations, experiences, and codes.