We’ve written before about the desperate need to improve our nation’s water infrastructure. In 2017, the American Society of Civil Engineers gave U.S. water infrastructure a “D.” Most of America’s water mains are made of legacy iron pipes, which are failing and causing more and more water main breaks. Now, a new report from the National Academies of Sciences raises questions about the connection between legacy iron pipe materials and Legionnaires’ disease, which directly affects more than 50,000 Americans each year.
The Problem with Metal Pipes
The report suggests that metal corrosion, especially iron, can promote colonization of Legionella, the bacteria responsible for Legionnaires’ disease. The authors of the study note that “[increased] bioavailability of various metal corrosion products, such as iron, may also upregulate virulence in legionellae, stimulate general biofilm growth, and contribute to Legionella growth in hot-water heaters.”
The link between iron corrosion and Legionella growth is especially concerning given the amount of water system components that are made from iron. Iron pipe, including both cast iron and ductile iron, is prone to corrosion over time when used in water infrastructure. And the report suggests that deteriorating iron water mains could pose a “habitat for bacterial proliferation”:
Much of U.S. water distribution systems consist of century-old unlined iron mains, which are beyond their designed lifespan and subject to substantial corrosion as well as intrusion during water main breaks. Corrosion of pipe surfaces provides not only a habitat for bacterial proliferation and protection from chlorine disinfectant residuals but also a source of nutrients.
Corrosion is a common problem that affects iron water mains as they age. So much so that the researchers conclude that “addressing the problem of legacy iron pipe is a critical engineering control to consider for Legionella.”
Some Good News: There are Other Options
Materials that have smooth surfaces and are resistant to corrosion have a substantially lower risk of harboring legionella. The researchers note that “stainless steel, PVC-C, and PVC-U [do] not enhance growth of L. pneumophila in these laboratory tests.”
It is estimated that between 52,000 and 70,000 cases of Legionnaires’ disease occur in the US every year. Controlling Legionella bacteria in our water systems is a vital public health priority, and the researchers noted that “[most] public water supply distribution systems consist of hundreds of miles of cast-iron mains, which will never be replaced in a time frame that would allow for better Legionella control.” For this reason, and so many others, municipalities are wise to consider non-metallic materials when updating their water infrastructure.