The Best Piping to Prevent Legionella and Biofilm Growth
What is the best piping for preventing or slowing the growth of Legionella or biofilm? It depends on whom you ask, but in general, it is the smoothest one. Smooth pipes make it difficult for biofilm to grow, which is where over 90% of Legionella and other pathogens are found. The chart below shows the relative smoothness of the inside of different piping systems when they are new, as well as copper piping after it has aged and oxidized.
Common nonmetallic piping systems such as cross-linked >polyethylene (PEX) and polyvinyl chloride (PVC) tend to be the smoother than ferric based piping systems. However, many don’t stand up to oxidants such as chlorine, chlorine dioxide and monochloramines, which are commonly used as disinfectants in the water. They can deteriorate or pit which creates a rough surface, which is ideal for Legionella and biofilm growth.
Galvanized and iron-based pipes were the standard for hot and cold-water piping prior to the 1950s and 1960s. The technology was patented in the 1830s. It replaced lead piping and was the standard for roughly 100 years. Ferric based piping systems start with a somewhat smooth interior but eventually rust, pit and corrode. They stand up well to heat but do not stand up well to oxidants in the water and eventually have the roughest inside surface of any of the piping systems making them the least desirable of all materials for Legionella control.
Copper piping has been the gold standard since the 1960s. It doesn’t rust and when it is new and has a very smooth interior surface, even smoother than most nonmetallic piping materials. However, over time it does oxidize, it can pit and the surface becomes very coarse, which is ideal for biofilm and Legionella growth.
Chlorinated polyvinyl chloride (CPVC) has a smooth surface and a high tolerance to oxidants put in the water for primary or secondary/supplemental disinfection. It’s resistance to disinfectants and ability to withstand higher temperatures makes ideal for reducing Legionella and biofilm growth for both cold and hot water piping systems. It maintains a a smooth surface over a long period of time.
Lastly, stainless steel maintains a relatively smooth interior finish over a long-time horizon, stands up to oxidants well and has a high heat tolerance. It is a good choice for biofilm control and Legionella proliferation prevention but isn’t commonly used for domestic or potable piping systems due to its relatively high cost.
The best piping systems to prevent Legionella and biofilm growth are below from best to worst.
- Stainless Steel
- PVC, PEX, Non-Chlorinated Plastic
- Galvanized, Iron