Cost and environmental impact are two reasons to install plastic pipes in buildings, but research shows they can put chemicals in drinking water and cause unpleasant odors.
Buildings are being plumbed with many types of plastic drinking water pipes. These include crosslinked polyethylene (PEX), high-density polyethylene (HDPE), polyvinylchloride (PVC), chlorinated PVC (cPVC), and polypropylene (PP) pipes, says Andrew Whelton, an assistant professor of civil engineering in Purdue University’s Lyles School of Civil Engineering and Division of Environmental and Ecological Engineering.
Plastic pipes are generally less expensive, lighter, and easier to install than metal pipes. A 2012 comparison showed PEX pipe was the least expensive among plastic pipes, costing just 43 cents per foot compared to the most expensive metal, copper pipe, at $2.55 per foot.
Thousands of dollars can be saved during construction by installing plastic instead of metal plumbing systems, and proponents assert plastic pipes require less energy to manufacture—generating less carbon dioxide compared to metal pipes—ostensibly making them a good fit for green buildings.
“Little is known about the degree to which plastic pipes sold in the US affect drinking water quality,” says Whelton, who will prsent the findings at the 2014 US Green Building Council’s Greenbuild International Conference & Exposition on Friday in New Orleans.
Six kinds of PEX pipe
Some testing results appear online in September in the journal Water Research. There, the researchers describe drinking water impacts caused by six brands of PEX pipes available in the United States.
For the Water Research study, researchers tested drinking water from a PEX plumbing system in a “net-zero energy” building in Maryland six months after the system had been installed.
The testing revealed the presence of 11 chemicals that were PEX pipe ingredients and ingredient degradation products. Research with PEX pipes in the laboratory also showed that six brands caused drinking water to exceed the US Environmental Protection Agency’s maximum recommended drinking water odor limit, Whelton says.
The US EPA’s maximum drinking water odor limit is a “threshold odor number” of 3, or 3 TON. Compliance is voluntary because the standard is based on aesthetic, not health, considerations.
Chlorine in the water
Odor and chemical levels were monitored with and without chlorine treatment over a 30-day period for the six pipe brands. Chlorine, the most popular disinfectant chemical used in the United States, protects drinking water from disease-causing organisms as it travels to the tap.
When chlorine reacted with chemicals leached by the plastic pipes, odor levels for one brand of PEX pipe tripled. While the total mass of chemicals leached by PEX pipes was found to decline after 30 days of testing, odors generally continued as the pipes aged, Whelton says.
A general assumption in the United States is that chemicals responsible for drinking water odors pose no health dangers. Although, several chemicals found in the plumbing research have regulated health limits, and one PEX pipe brand caused drinking water to exceed the ethyl-tert-butyl ether (ETBE) drinking water health standard. ETBE is a PEX pipe manufacturing byproduct with drinking water standards in New Hampshire and New York state.
When establishing the ETBE limit in New Hampshire, public health officials specifically added a 10-fold reduction to allow for its suspected carcinogenic potential. However, no federal drinking water standard exists, Whelton says.
The researchers found ETBE drinking water levels as high as 175 parts per billion (ppb) during the first three days of PEX pipe use and then 74 ppb after 30 days of use when the testing ended. New Hampshire has the most stringent drinking water health standard of 40 ppb. Michigan also has an ETBE standard, but it is based on limiting drinking water odor caused by ETBE.
Smells like gasoline
The presence of drinking water odor can prompt homeowners to avoid their drinking water altogether.
“A contractor who installed PEX in parts of a million-dollar home in Oklahoma asked us for help because the homeowners reported gasoline-like odors in a bathroom’s tap water,” Whelton says. “The homeowners refused to take showers in the PEX-plumbed bathroom because they were concerned about their health.”
By testing tap water from the home, Whelton’s team discovered that toluene, a solvent used for plastic resin synthesis and ETBE were present above levels where odors would be detected. Neither toluene nor ETBE exceeded health standards, however. The gasoline smelling water was safe to use.
The research also shows that there are differences in the quality of PEX products on the market, and different brands cause different odor and chemical-leaching impacts.
The team plans to continue the work and release additional results from the study over the next several months. Findings show some chemicals released by plumbing pipes can be transformed into carcinogenic chemicals regulated by the EPA; chemicals leached by certain plastics are conducive to bacterial growth; and plumbing system cleaning practices described in some, but not all, plumbing codes can cause PEX pipe chemical leaching to worsen.
The work is funded by an NSF grant.
Source: Purdue University