Lead in U.S. Drinking Water
Drinking water is tightly regulated in the United States and, for the most part, is remarkably safe. Recent contamination episodes in Flint, Michigan, and elsewhere, however, have highlighted the fragility of this public health success story and the serious health risks lead poses in significant portions of the U.S. drinking water supply. Exposure to lead, even at low levels, has adverse health effects for people – especially children, pregnant women, and their developing fetuses. While these risks are widely known, lead continues to pervade the tap water of many American communities. This is due largely to the extreme difficulty and high cost of identifying, locating, removing, and preventing the many potential sources of lead across thousands of U.S. water systems, which vary widely in size, type, age, source supply, ownership, and maintenance.
The lead problem
In the United States, lead enters drinking water primarily through leaching from corroded pipes and plumbing fixtures that contain lead. Physical disturbances to these materials can also sometimes release lead particles into drinking water.
Lead pipes were widely used in water-supply systems until the early 20th century, when many communities began to recognize the health effects of lead exposure. Use of lead-containing solder, service lines, and plumbing components, however, continued through the mid-1980’s.
In 1986, these were banned from use in new U.S. plumbing systems, but they remain throughout much of the country’s drinking water infrastructure, which largely pre-dates the ban.
Until 2014, plumbing fixtures with as much as 8% lead-by-weight could be legally labelled “lead free”. While the allowable percent is now reduced to 0.25%, fixtures installed prior to the revision remain in use throughout the country. Because of the way lead-by-weight averages are calculated, even some newer fixtures can release significant concentrations of lead.
Roughly 87% of the U.S. population receives water for household use from “public water systems” – defined as those serving on average at least 25 people for at least 60 days per year. More than 150,000 of these systems exist in the United States in a range of sizes. They can be owned publicly or privately (despite their name), and typically draw from either groundwater sources such as wells or surface water sources such as rivers, lakes, and reservoirs.
The diversity of systems and their varying degrees of upkeep means there can be no one-size-fits-all approach to identifying and removing lead from all drinking water systems.
In recent surveys by the American Water Works Association, nearly a third of U.S. water systems reported service lines containing lead. The total number of lead service lines in the United States is estimated to be upwards of six million.
A single plumbing fixture containing lead can contribute to contamination of tap water, even when associated larger water mains and service lines are fully lead-free.
Because it is virtually impossible to monitor all fixture types and uses at the individual building and household level, the full extent of lead sources across U.S. water systems is unknown.
Consumers generally cannot see, taste, or smell lead in their drinking water. The only way to know whether tap water contains lead is to test it.
While individual filtration systems can be used to remove lead from drinking water at the tap, there are several barriers to their widespread use, including a lack of consumer awareness about whether their drinking water is indeed contaminated, the need to install and replace filters correctly, and the cost of purchasing and regularly replacing filters at each point of use.
Drinking water is just one pathway for people to become exposed to lead. Others include deteriorating paint and household dust containing lead; older painted toys, furniture, and jewelry; lead-glazed pottery; and lead-contaminated soil or air, among others.
There are several well-established adverse health effects of lead exposure, even at low levels. Young children, pregnant women, and their developing fetuses are especially vulnerable to these risks.
Among the known health effects for children are lower IQ, slowed growth, behavior and learning problems, anemia, and hearing problems.
Studies have also suggested that children who do not display overt symptoms may still experience lead’s effects later in life, though it can be difficult to distinguish between the effects of early lead exposure and other correlates, such as poverty. Multiple studies have identified a relationship between early childhood lead exposure and future violent behavior or criminal activity, for example, but such observational studies are not designed to prove direct causality.
Lead can also accumulate in human bones over time. During pregnancy, lead is released from the mother’s bones, along with calcium, and used in fetal bone formation. A fetus can also be exposed to lead from across the placental barrier. These exposure pathways can result in premature birth, gestational hypertension, reduced fetal growth, and fetal death.
Breast milk is another pathway of lead exposure for infants. Lead released from a lactating mother's bones can exit the body via breast milk.
In adults, chronic low-level lead exposure has been linked to cognitive decline, hypertension, and adverse reproductive outcomes, among other health effects.
Lead levels in children
The most common test for lead exposure in people is a blood test measuring micrograms of lead per deciliter of blood—a person’s “blood lead level”.
The Centers for Disease Control and Prevention (CDC) sets and periodically updates a “reference level” for lead in children’s blood based on large national surveys of children’s health.
The reference level aims to delineate the 97.5th percentile, or top 2.5%, of children in the United States with the highest levels of lead in their blood. The CDC’s current reference level is 5 micrograms per deciliter.
Importantly, this is not a safety threshold demarking a point below which there are no health risks (recall—no level of lead in blood is considered safe). Rather, it is a marker used to track exposure trends and indicate children with blood lead levels that are elevated compared to the national average and who are thus at the highest risk for health effects.
For context, the blood lead level at which medical intervention is recommended for children is 45 micrograms per deciliter. (The most common medical treatment is chelation therapy – an intravenous infusion that binds to and helps remove toxins from the blood.)
Below this level, the risks of chelation generally outweigh the benefits, and management strategies typically focus on identifying and on removing or minimizing the primary source of exposure.
Overall, blood lead levels in U.S. children have been declining for several decades—with some of the steepest reductions achieved following regulatory action in the 1970s, 80s, and 90s to phase out leaded paint and gasoline.
- More recent scientific studies that emphasize the health risks of low-level lead exposure, especially in children, underscore that despite these important improvements, children continue to be exposed to lead through deteriorating lead-based paint and, in some places, through drinking water.
Rules and regulations
The 1974 Safe Drinking Water Act (SDWA) requires the U.S. Environmental Protection Agency (EPA) to establish and enforce health-based safety standards for all public water systems.
Enforcement of these standards is primarily carried out by individual states through various methods of water-system monitoring and reporting.
When monitoring identifies the presence of a contaminant at a level above the SDWA safety standard, states and the EPA must work with utilities to reduce or remove the contamination and notify consumers.
For most contaminants regulated under the SDWA, the EPA sets a safety goal called the Maximum Contaminant Level (MCL) – a level below which there are no known or expected health risks to people over a lifetime of exposure.
For lead and copper – which can contaminate a water supply based on plumbing fixtures in individual homes and private plumbing systems (and are thus impossible to fully control at the water-system level) – the EPA instead established an enforceable monitoring and treatment strategy for water systems to help control corrosion and reduce leaching from plumbing.
When testing shows that more than 10% of customer taps in high-risk homes in a given water system (such as those known to be connected to lead-containing service lines) exceed lead concentrations of 15 parts per billion (ppb), the system must install or improve corrosion control treatment.
Corrosion control most often involves introducing chemical treatments to make the water supply less corrosive or to facilitate the buildup of protective scales inside water pipes, which reduces leaching of lead. These requirements are laid out in the 1991 Lead and Copper Rule, which is currently under consideration for revisions.
While the Lead and Copper Rule establishes a public health goal of zero lead in drinking water, this standard is unattainable and unenforceable because:
There are many household-level or privately-owned sources of lead that cannot be controlled by public water systems.
Lead releases can vary significantly between taps in a single household and may not be reflected by sampling of associated water mains.
There is no complete chemical fix that utilities can use to fully stop the corrosion and lead-leaching process.
Lead continues to pervade old plumbing systems and be added (albeit in declining quantities) to new plumbing systems.
LAST UPDATED February 22, 2019
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Key references for those who want to dig deeper
Where the lead is and what can be done about it:
In 2017, the Robert Wood Johnson Foundation and The Pew Charitable Trusts issued 10 Policies to Prevent and Respond to Childhood Lead Exposure, a report assessing risks for childhood lead exposure in the United States and available policy approaches to address the challenge. Among the report’s key findings is that removing lead service lines from the homes of children born in 2018 would protect more than 350,000 children and yield $2.7 billion in future benefits, while the cost of replacing these lead pipes would cost an estimated $2 billion.
In 2016, the U.S. EPA issued, Optimal Corrosion Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public Water Systems, a technical paper outlining recommended corrosion control techniques utilities can use to comply with requirements of the Lead and Copper Rule.
In 2016, the Journal of the American Water Works Association published a National Survey of Lead Service Line Occurrence, summarizing survey data about the prevalence of lead service lines across water systems in different cities and regions of the United States. Approximately 30% of surveyed water systems reported the existence of lead service lines, and the paper’s authors estimate there are at least 6.1 million lead service lines across America’s community water systems.
In 2006, the National Academies of Sciences, Engineering, and Medicine issued Drinking Water Distribution Systems: Assessing and Reducing Risks, a comprehensive overview of water distribution systems in the United States and key challenges to upgrading and maintaining these systems. Among the report’s chief recommendations is to fund more research and data collection on “premise plumbing” – or plumbing in privately owned building and homes – which the authors highlight as an important source of drinking-water quality problems that is not well managed or understood.
In 2000, the American Water Works Association Research Foundation (a nonprofit dedicated to research that can help utilities respond to and comply with regulatory requirements) issued, Lead Pipe Rehabilitation and Replacement Techniques, summarizing the state of technology for restoring and replacing lead pipes in America’s water distribution system. Among the report’s key recommendations is to locate, with urgency, all lead service lines in the United States.
In 2016, the American Academy of Pediatrics issued, Prevention of Childhood Lead Toxicity, outlining the scope of child lead exposure in the United States, its health impacts, and management guidance. The report asserts that there is no safe level of lead in blood.
In 2012, the National Toxicology Program of the U.S. Department of Health and Human Services issued Health Effects of Low-Level Lead. The report finds that there is sufficient evidence for adverse health effects of lead, even at low levels.
A 2012 Committee Opinion on Lead Screening During Pregnancy and Lactation by the American College of Obstetricians and Gynecologists outlines the available evidence related to lead exposure and maternal-fetal health. While the opinion does not recommend routine blood-lead testing for all pregnant women, it recommends steps for pregnant and lactating women whose blood levels exceed certain thresholds.
A 2012 paper, Lead in Drinking Water and Human Blood Levels in the United States, published by the National Center for Environmental Health at the Centers for Disease Control and Prevention, reviews the health effects of water-lead exposure and highlights the vulnerability of children to neurodevelopmental impacts. It also provides a historical overview of blood lead levels and trends in the United States.
In 2011, the National Bureau of Economic Research issued a working paper, Cognitive Disparities, Lead Plumbing, and Water Chemistry, outlining the cognitive health impacts of water-lead exposure. This study is one of just a few looking at such effects in a large population – which is difficult due to the many pathways of possible exposure and the tendency of populations to self-select into areas with different levels of lead contamination – and presents evidence of a link between water-lead exposure and intelligence.
A 2008 paper, Association of prenatal and childhood blood lead concentrations with criminal arrests in early adulthood, in PLOS Medicine, links elevated prenatal blood-lead levels with higher rates of violent offenses later in life. This is one of the first studies to link lead exposure at the developmental stages to adult criminal behavior, though direct causality remains to be proven.
A 2004 paper, Lead Poisoning, in the Annual Review of Medicine, outlines the science of lead toxicity and the health effects of lead exposure, including cognitive and behavioral impacts, neurodevelopmental impacts, and the impacts of lead exposure in older individuals.
Broader evaluations of U.S. drinking water infrastructure:
Each year, the American Society of Civil Engineers issues an Infrastructure Report Card for the United States – an assessment made by a committee of civil engineers, in consultation with technical and industry experts. In 2017, the ACSE scored U.S. drinking water infrastructure at the “D” level.
In 2014, the U.S. Geological Survey issued Estimated Use of Water in the United States in 2010, a report released every five years highlighting American water use trends. The report summarizes domestic water use trends in the United States, including sources, quantities, and the landscape of distribution/collection systems.
In 2013, the U.S. EPA released The State of Technology for Rehabilitation of Water Distribution Systems, outlining the available technologies for rehabilitation and upgrade of aging water systems in the United States. The report also summarizes the characteristics of U.S. water supply systems and identifies gaps in data about pipe conditions.
In 2012, the American Water Works Association released Buried No Longer: Confronting America’s Water Infrastructure Challenge. The authors estimate that the total cost of upgrading and expanding America’s water systems to meet the needs of the U.S. population is at least $1 trillion over the next quarter century.