In April 2014, footage surfacing of fetid, brown water flowing from sinks in Flint, Michigan, brought the real threat of lead exposure to America's attention.
However, a recent analysis of Environmental Protection Agency (EPA) data revealed that Flint is far from the only city in the U.S. plagued by dangerous levels of lead in its drinking water.
According to the Natural Resources Defense Council (NRDC), more than 18 million Americans were served by 5,363 community water systems with lead violations in 2015.
A total of 1,110 of those water systems, which collectively serve 3.9 million people, showed lead levels in excess of 15 parts per billion (ppb) in at least 10 percent of homes tested.
Though public health officials say that no levels of lead should be considered safe, the 15 ppb-mark is the action level set by the EPA.
In Flint, Michigan, lead-contaminated water resulted when the city's water supply was switched from Lake Huron to Flint River, which contains highly corrosive and polluted water, without first treating the lead pipes.
As these pipes corroded, lead levels soared as high as 10,000 ppb in some locations.
Despite widespread media coverage of the crisis and recent criminal indictments filed against state and local officials, Michigan's Department of Environmental Quality still had not officially reported Flint to be in violation of the Lead and Copper Rule as of June 2016, according to the NRDC report.
"Even though we know that there are egregious problems happening with Flint with lead for years and years now, it didn't show up as having any issues with lead in the EPA database that we used," NRDC Staff Scientist and co-author of the report Kristi Pullen-Fedinick said.
"Again, when we think about cities like Flint not being there, 18 million people served by over 5,000 systems is likely to be an underestimate. And so, we can't even necessarily say how big the problem really is."
According to the NRDC report, all 50 states had at least one water system in violation of the lead and copper rule in 2015.
Additionally, states and the EPA took formal enforcement action against just 11.2 percent of the over 8,000 violations that year-leaving 88.8 percent free from any formal enforcement action.
"I was really shocked first to see the pervasiveness, how widespread these issues with lead really were," Pullen-Fedinick said. "But then really looking at the enforcement issues, so seeing that so few of the violations face any real enforcement action at all is really just shocking on a lot of levels."
The gross lack of enforcement can be attributed in part to severe understaffing of the EPA at the federal level, she said.
Underreporting, however, may be due to a variety of issues, including bad or unreliable testing methods and testing in houses not served by lead service lines.
In early May, President Obama spoke to a crowded gymnasium in Flint, Michigan, urging parents of the city to have their children tested for lead exposure.
Lead exposure can have damaging and life-altering consequences, even at low levels. Children and babies are most at risk, with side effects including developmental delay, learning difficulties and slowed growth, according to the Mayo Clinic.
Only one month before Obama's visit, lawyers representing Flint residents filed a $220.2 million damages claim alleging that negligence on the part of the EPA had contributed to the city's dangerous lead levels, according to Reuters.
"We need to fix Flint. The people in Flint have been suffering unnecessarily for years, and so we really need to make sure that our members of congress and that state of Michigan provide the monetary resources that the people in Flint really need in order to ensure that when they turn on their water and give a glass of water to their child, they know that water is safe," she said.
"And we also need to fix infrastructure in this country. Our infrastructure is crumbling around us."