Flint, Mich. isn't the only city with severely contaminated water that's making national headlines. A new report finds that even more Americans might be living with contaminated water than we previously believed.

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In a report released Tuesday by the National Resources Defense Council, researchers found that in 2015 "18 million Americans are drinking tap water from water systems that have violated federal rules for lead safety."

According to the report, 5,363 water systems were found in violation of the Environmental Protection Agency's Lead and Copper Rule, "a federal requirement for monitoring of lead and copper levels in water," Vox reports.

Specifically those violations "include failure to properly test water for lead, failure to report contamination to residents, and failure to treat water properly to avoid lead contamination," according to CNN.

In the map below, you can see where those communities are located.

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Elevated lead levels in water were discovered in 10 percent of the houses tested in 1,110 communities that serve 3.9 million people, including Portland, Ore. to Passaic, N.J., according to the NRDC report.

But what's even more troublesome is that the city of Flint is not listed as in violation of the EPA's water system rule. Despite public knowledge of the water contamination in Flint, it is has yet to be reported in the EPA's database.

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"This glaring omission illustrates the serious problem of underreporting and gaming of the system by some water supplies to avoid finding lead problems, suggesting that our lead crisis could be even bigger," the report's authors wrote.

But this is not necessarily surprising.

According to CNN, the EPA knows about the many violations but does a poor job at enforcing its own rules. In fact, "in 9 out 10 cases the EPA took no enforcement action when water systems violated the Lead and Copper rule." In addition, Alissa Walker from Gizmodo reported that out of all the violations, the EPA has only "followed up with 11 percent of the violations."

"Imagine a cop sitting, watching people run stop signs, and speed at 90 miles per hour in small communities and still doing absolutely nothing about it -- knowing the people who are violating the law. And doing nothing. That's unfortunately what we have now," Erik Olson, health program director at the Natural Resources Defense Council, told CNN in a video report.

ATTN: reached out to the EPA but did not receive a comment in time for publication.