NSF-Supported Researcher Discovers Link Between Water Treatment Practices, Corrosion of Home Plumbing, and Elevated Lead Levels in Drinking Water

 

NSF-supported investigator Marc Edwards, Professor of Civil and Environmental Engineering at the Virginia Polytechnic Institute and State University, has completed the first laboratory experiments demonstrating that changes in water chemistry alone are sufficient to cause pinhole leaks in copper tubing in drinking water distribution systems. An outbreak of such leaks began in home plumbing systems in the suburbs of Washington, DC and elsewhere in the late 1990s, costing consumers billions of dollars per year for repair and replacement. While investigating the causes of these leaks, Edwards discovered very high levels of lead contamination in DC area drinking water and designed new sampling procedures for testing drinking water to measure more accurately the degree of lead contamination. Environmental exposure to high levels of lead can seriously impair virtually all aspects of mental and physical functioning, especially the rapidly developing neurological systems of young children.

 

One of the world’s leading authorities on lead and copper corrosion, Edwards first predicted in 1994 that emerging changes in drinking water treatment practices could result in increased corrosion and formation of pinhole leaks in copper pipes, which are used in 80 percent of home plumbing systems in the United States. Since the late 1990s, when these water treatment changes became widespread, he has tracked outbreaks of pinhole leaks in homes in several states, including Alaska, California, Florida, Maryland, Massachusetts, Ohio, South Carolina, South Dakota, Tennessee, and Virginia as well as the District of Columbia. While the cost of corrosion in home plumbing systems is not precisely known, Edwards estimates that it is of the same magnitude as corrosion of public drinking water infrastructure, or about $16 billion per year.

 

Pitting corrosion—a type of non-uniform corrosion that causes pinhole leaks in copper plumbing—is a poorly understood phenomenon. With support from NSF, Edwards has studied the complex processes and environmental factors that govern pitting corrosion in drinking water distribution systems. “Without question, there is no way that I would have been in a position to uncover these problems and speak out about them without the support of NSF, which enabled me to develop the fundamental science behind these issues,” he noted. “The relatively high burden of proof that science requires would not have been met. To my knowledge, no agency other than NSF is funding research on the impacts of changing drinking water chemistry on home plumbing infrastructure.”

 

Over the course of 8 years of research, Edwards and three graduate students identified the specific factors in drinking water chemistry associated with increased pitting corrosion in copper pipes: increased concentrations of chlorine and aluminum, decreased concentrations of natural organic matter (from decaying leaves and other sources), and higher pH levels. These factors correspond closely to altered water chemistry that followed significant changes in treatment practices to meet new federal drinking water standards in the late 1990s. Edwards’ research also showed that other factors thought by some to cause pinhole leaks—such as poor plumbing practices, stray electrical current, and lightning—were not required to induce the phenomenon.

 

Several of Edwards’ findings surprised many people. For instance, the role of the higher pH levels often required to meet new drinking water standards was unexpected, since metal corrosion normally takes place in an acidic (low pH) environment. The role of aluminum as a catalyst of pinhole corrosion was surprising because elevated aluminum levels are not necessarily present in drinking water as it leaves the water treatment plant. However, forensic analysis by Edwards and his team detected an aluminum compound scattered over the inner surfaces of copper pipes. The source of the aluminum could be leaching from the cement linings of public water distribution pipes (Portland cement is 4 percent aluminum by weight) or aluminum-based chemicals used to remove organic matter from drinking water.

 

Also surprising were the very high lead levels detected in Washington, DC tap water. While the federal safe limit for lead is 15 parts per billion, at one DC home the readings were off the scale of Edwards’ field meter, that is, in excess of 1,250 parts per billion. He discovered that traditional testing procedures, which measure lead levels in the first draw (first water out of the tap) and 5-minute draw, understated the potential lead exposure. Edwards tested samples drawn at various intervals and found the highest lead levels in the 1-minute draw, which usually has the longest contact with lead-containing plumbing materials. In response, he designed a revised sampling plan for use by Washington, DC water utilities to clearly define the true magnitude of the lead problem in drinking water.

 

Edwards’ experimental results also showed that the release of lead in Washington, DC drinking water was caused by a galvanic (battery) reaction between lead and copper. He called attention to the fact that partial replacement of lead service lines—which fulfills the letter of law for remedial action required when high lead levels are detected in drinking water—could actually increase lead releases in drinking water. This is because replacing some of the existing lead pipe with fresh copper pipe and connecting it to copper plumbing in households is likely to promote higher rates of galvanic reaction between lead and copper, leaving behind a much worse problem for consumers than if nothing had been done at all. Edwards has called for increased scrutiny of such partial replacements.

 

The goal of Edwards’ ongoing research is to enable scientists and engineers to rationally predict and prevent problems with pinhole corrosion. With current support from NSF’s program on Materials Use: Science, Engineering and Society (MUSES), Edwards works with a multidisciplinary team investigating the broader economic, social, and health aspects of materials failure in drinking water infrastructure.

 

Edwards testified in March 2004 before the U.S. House of Representatives Committee on Government Reform on lead in Washington, DC drinking water. In April 2004, Time magazine named Edwards an Innovator and one of the most influential people in the nation on the future of water resources issues. He was a 1995 recipient of an NSF Presidential Faculty Fellowship.

 

For more information, contact Marc Edwards at edwardsm@vt.edu, (540) 231-7236. See also articles in Materials Performance (May 2004 and December 2002) and Chemical and Engineering News (vol 81, no 33, pp. 51-53).