Water Sampling Differences Lead to Flawed Risk Assessments
By Kelly A. Reynolds, MSPH, PhD
As more information is being released about the Flint, MI waterborne contamination event, new questions arise as to what officials knew about the water quality, or lack thereof. While accusations of blame continue to mount, standard methods of water quality assessment are also under broader scrutiny. In order to accurately assess consumer risks of exposure to waterborne contaminants, information about water use patterns and behaviors are important to consider in addition to contaminant concentrations.
Drinking water travels a lengthy and often complex route from the source, through the treatment works, to the distribution system and finally, to the consumer’s tap. Municipal water suppliers have a responsibility to monitor water quality throughout its lifetime, with particular attention to points of vulnerability, to ensure safety for the end user. Part of this monitoring scheme is designed to identify critical points of control where contamination is most likely to occur. Lead pipes used in service lines that distribute supply from the water main to homes are known to be the primary source of waterborne lead exposures. When these lines are disturbed (i.e., repaired or replaced) either by the water utility or the homeowner, lead may leach into the water supply at increased levels. Even more challenging is the fact that each municipal water system is unique and must be assessed individually for potential problems in terms of treatment or corrosion-control needs. Changes in the source water, treatment, storage or distribution requires advanced assessment and post-change reassessment to ensure the supply meets federal primary and secondary contaminant limits. As we’ve learned from the Flint disaster, such efforts are not always applied or effective.
Controlling lead exposures
US EPA recommends a variety of actions consumers can initiate to reduce lead exposures, including flushing pipes before drinking, using only cold water to drink and having the water tested.1 The first directive is to flush cold-water pipes by turning on the water until it runs as cold as it can. This could take anywhere from five seconds to two minutes or more. (In my home, it takes about 30 seconds.) This is particularly important if tap water has been sitting in the premise plumbing for more than six hours, during which time significant amounts of lead could leach into the water from surrounding pipes. In addition to time, temperature is a factor as heat generally increases the rate of leaching. For this reason, only water from the cold tap should be used for drinking and food preparation.
US EPA’s final directive is for consumers to have their water tested for lead. While this may help one identify a need to mitigate a chronic problem, intermittent or temporary events may go unnoticed if they occur outside of targeted sampling days. Even short-term exposure to lead or other waterborne contaminants can pose a serious health risk to consumers. Sometimes aesthetic changes are noticeable in water (i.e., different taste, odor or color) and may prompt consumers to test their water. In the case of Flint, it would be months before residents linked changes in their water to harmful lead exposures.
Trusted testing or not?
One of the concerns with water testing, whether from routine monitoring practices or during suspected peak events, is consistency in the sampling method. US EPA has published federal guidelines for public water system sampling requirements under the Lead and Copper Rule (LCR). It requires utilities to preferentially target homes with lead plumbing for their compliance monitoring and to take first-flush samples for a worst-case scenario sampling. Which homes are monitored is another potential loophole where homes with high levels of lead may be dropped from the sampling list when they should be more heavily targeted. According to a 2004 Washington Post investigative report, such cherry-picking of sample locations corresponded to an average reduction in lead levels during a 2002 survey in Portland, OR.2
Lee-Anne Walters, the mom who helped to expose the lead disaster in Flint, reported sampling differences in her own home when comparing methods of city inspectors and those of a university laboratory, which dramatically impacted lead results. These differences in lead concentrations were outlined in her recent Congressional testimony: “I had three tests done by the city of Flint, using extra steps that tend to minimize lead in water. Those numbers were 104 ppb, 397 ppb and 707 ppb,” compared to independent testing from Virginia Tech University, that collected 30 samples: “My average water lead was 2,500 ppb and my highest was 13,200 ppb.” Walters and others involved in the testing cited method loopholes that minimized exposure concentration estimates, including a preflushing step.3
Variable conditions matter
Other variable sampling conditions include having the presence of a faucet aerator, which can collect lead particles over time that slough off during sampling. Transferring initial samples to smaller containers can potentially leave settled lead particles behind. Sampling from cold water faucets, although the most likely source of drinking water, is not the most cautious approach; more lead is leached from hot water use, which is often the source for cooking and preparing baby formula. Low-flow sampling can lead to less sloughing of lead particulates compared to heavier flows. Time in residence must be considered for water samples where lead concentrations increase with a lengthened absence of water use.2,4
Addressing these and other concerns, US EPA is developing long-term revisions to the Lead and Copper Rule. Beginning in 2014, the National Drinking Water Advisory Council LCR Working Group convened to discuss sample site-collection criteria and lead-sampling protocols. These meetings have produced a series of white papers with one focused on sample site selection. Current criteria calls for collection of one-liter, first-draw samples from taps but does not prioritize sampling from lead service lines, the greatest (percent-wise) contributor of lead sources in water. Depending on the source of the lead (i.e., service lines versus premise plumbing), sequential draw samples could result in higher lead concentrations. Understanding details of the water delivery chain and potential lead sources can help to identify worst-case sites to target.
Faulty infrastructure, economic concerns and diminishing supplies dictate changes in the water delivery chain that may continue to cause unforeseen harmful exposures. Whether due to mistakes, misunderstandings or malice, there will likely be another Flint experience. Relying on consumers to change behaviors to minimize lead exposures adds a level of uncertainty in risk management. Although flushing has been shown to lower water and blood lead levels, this solution may not be effective or sustainable. Determining accurate flush times and contradicting inherent thoughts on water conservation are known barriers.
Consumers, in their search for safe water, will continue to have a level of responsibility in the overall process. POU devices certified for specific contaminant removal offer a proactive approach to reduce exposures and minimize risks for known and unforeseen hazards. Water treatment professionals are consumers’ first line of defense in preventing harm to their family, should an emergency occur.
Flint is an example, and a wake-up call, of how exposures may occur and continue unnoticed for long periods of time. POU devices, however, are not passive treatment tools. Failure to maintain POU filters can result in exposure to contaminants in much greater concentrations than have ever been found in municipal water supplies. As with municipalities, proper assessment of treatment needs and system maintenance is essential with POU devices.
- US EPA, “Lead in your drinking water,” EPA/810-F-93-001, 1993. [Online]. Available: http://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=20001R4V.txt. [Accessed: 15-Feb-2016].
- Renner, R. “Exposure on tap: drinking water as an overlooked source of lead,” Environmental Health Perspectives, Vol. 118, No. 2, pp. A68–72, Feb. 2010.
- Walters, L.A. “House Democrats Hold Hearing: ‘The Flint Water Crisis: Lessons for Protecting America’s Children’.” [Online]. Available: https://www.youtube.com/watch?v=1fGFC_IwSm8. [Accessed: 16-Feb-2016].
- Edwards, M. “Lead in drinking water: sampling variability and analytical issues,” Presented at the American Public Health Association annual meeting, Philadelphia, PA, 2009.
About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at firstname.lastname@example.org