America is replacing its pipes: Is ductile iron pipe a good alternative for plastic?

Across the U.S., there are more than 2 million miles of water pipes installed beneath our feet and out of sight — and they’re getting old.

According to the U.S. Environmental Protection Agency (EPA), there are 240,000 water main breaks each year and over the next two decades, it’ll take about $420 billion to repair and improve the nation’s water distribution and transmission systems. In addition to aging pipes there are those that pose clear health risks: In 2021, Congress allocated $15 billion specifically for replacing lead service lines. The decision that municipalities across the country will face now is what type of pipe material they should use to replace the old ones.

Plastic pipes, like polyvinyl chloride (PVC), tend to be less expensive than established metallic pipe materials like ductile iron pipe (DIP). In 2017, Bluefield Research, an advisory firm focused on water, projected that up to 80% of municipal investment in water pipes over the next decade could go to plastic. However, there are mounting concerns about toxic material leaching from this type of pipes, further complicating the calculation for municipal decision makers trying to manage the financial, environmental and health impacts of water infrastructure materials.

Like so many communities across the country, owing to its affordability, PVC pipes became a favorite in Prescott, Arizona, in the 1980s.

“Developers decided to use PVC because it’s cheap,” Steven Olfers, the city of Prescott’s Utilities Manager, told Environmental Health News (EHN). “It’s a cheap capital expense compared to [ductile iron pipe].”

But now Prescott is pulling the plug on PVC. The city’s mayor told residents in a New Years letter that they would use ductile iron pipe going forward for water mains—those are the large pipes that carry water into communities, while service lines are the smaller ones that carry it from mains into homes and buildings. While copper, stainless steel and various plastics are options for builders working on service lines, ductile iron and plastics like PVC are the major options for municipalities considering mains. Prescott’s chief concern for their pipes, Olfers said, was durability.

PVC piping

PVC pipes Arizona

“We’ve had a large number of failures on PVC pipes that are fairly new,” he said. “Rocky soils and areas around here just wreak havoc on that stuff.”

The mayor’s letter stated that the city’s cost for ductile iron pipe is $36.00 per linear foot, while PVC is $33.50. In Prescott, that cost is made up for by longevity, the letter stated: where ductile iron typically lasts between 60 and 80 years, PVC only lasts 20 to 30 years.

“I cannot speak for other utilities, but for potable water in non-corrosive soils, ductile is the way to go,” Olfers said. “It offers [a] long life with low maintenance.”

Prescott’s decision to move away from plastic was based largely on their unique geology. Andrew Whelton, a professor of civil, environmental and ecological engineering at Purdue, told EHN that leaders across the country need to consider a myriad of factors like their environment, the makeup of their water and the specifics of the materials they’re considering. And there aren’t a lot of great resources to help them do that.

“It’s unique to each community,” Whelton said. “There’s been no comprehensive effort to understand how this all fits together, so that utilities can make decisions.”

Although the data is murky, on the whole, there seems to be less concern among experts and advocates with DIP and other metal pipes leaching dangerous chemicals into our drinking water than with PVC and other plastics.

Health concerns for PVC pipes

Given the material’s relatively young age, there are lots of unanswered questions surrounding plastic pipes. Last year, a report from Beyond Plastics, the Plastic Pollution Coalition and Environmental Health Sciences* highlighted research that has identified dozens of toxic chemicals released into water by PVC and chlorinated polyvinyl chloride (CPVC) pipes. It also stressed that there is a lack of data on these chemical leaches into drinking water in “real world” settings.

“We don’t have a very good public understanding about the chemicals that are leaching out of a lot of the plastics that we install in our infrastructure,” Whelton said. “PVC pipes are used throughout the United States. And it’s a risk that we all face, drinking water from materials that we haven’t necessarily tested thoroughly.”

What complicates matters, Whelton said, is a lack of transparency with the testing and safety certification of plastic pipes. Those certifications are handed out by third-party organizations such as NSF.

PVC pipes health risk

“The plastics industry manufacturers pay an industry-backed organization to do their testing behind closed doors and issue them certification,” Whelton said. “There’s a deeper systemic problem.”

Despite assurances from certification bodies, Whelton points out that there have been incidents that illustrate what can go wrong with plastic pipes. Since 2017, there have been at least 12 documented examples where wildfires have heated plastic pipes and caused unsafe amounts of chemicals such as benzene — a carcinogen that can also cause immediate health problems — to leach into water.

Iron, on the other hand, does not come with the same uncertainty.

“Iron has been used for centuries. We know a lot about [it],” Whelton said. “Plastics have only been used for water systems since the 1960s.”

In fact, iron pipes have been used since at least the 1600s, when Louis XIV had them installed in the Palace of Versailles.

“I am generally more comfortable choosing metal pipes because there is more known about them,” he said.

Advantages of ductile iron piping 

Marc Edwards, a water treatment expert and professor at Virginia Tech University who played a central role in uncovering the Flint, Michigan water crisis, has also looked closely at ductile iron pipes. This type of pipe uses a liner on the inside, or else it will rust, and that choice of liner is a critical concern from a health perspective because it is what the water actually comes into contact with. Edwards co-authored a paper that examined cement-lined iron pipes, which is what they are using in Prescott.

“What we found is that in most circumstances, ductile iron with cement linings are very resistant to corrosion and they don’t leach appreciable quantities of anything to the water,” he told EHN.

An important caveat Edwards mentioned is corrosivity. Very “soft” water, which is more acidic, may be able to corrode the cement lining over time, which could ultimately lead to rusty pipes and discolored water. According to its most recent water quality report, Prescott’s water was categorized as “moderately hard.”

In general, Edwards feels pretty good about the health impacts of today’s plumbing materials, even plastics, which he mentioned has improved considerably in recent decades.

“There’s no perfect material. They all leach something into the water,” Edwards said. “The most important things in my mind are cost, performance and safety. And of those three, safety right now is the least of my concerns, given the data I’ve seen.”

Even beyond safety, Paul Hagar, executive director of Safe Piping Matters, told EHN there are “clear advantages” with ductile iron. Metal pipes like ductile iron and copper are recyclable, whereas plastic, he said, is “landfilled or incinerated” at the end of its life. Ductile iron pipes are typically made of at least 90% recycled material and are fully recyclable themselves, according to the Ductile Iron Pipe Research Association (DIRPA). However, a recent study that compared the environmental impact of various plastic goods and their alternatives found that ductile iron pipe has a greater climate change impact than PVC, citing its greater weight and the greenhouse gas emissions involved in its transportation and installation.

When it comes to cost, while DIP is more expensive than PVC up front, the metal pipe is more cost-effective over its service life, according to a study (which was funded by DIRPA) by researchers at the University of Michigan. That finding resonates with Prescott’s decision making process, although their rocks might have made the choice easier.

Hagar added that although there are open questions about the health impact of plastic pipes, they are “certainly contributing at some level to the chemical and microplastic load that our bodies are having to flush.” And until we have clearer insight into how these pipes impact our water and health, the debate over how to repair our vast national pipe system remains hazy.

“It truly comes down to cost and if you’re comfortable with the unknowns associated with plastics,” Whelton said. “And if not, well, are you willing to pay the added costs associated with the alternatives?”

*Editor’s note: Environmental Health Sciences publishes, which maintains editorial independence.