A new report from the Natural Resources Defense Council has found that close to 77 million Americans were supplied with water in 2015 that violated drinking water standards.
This included 18 million Americans who received water containing levels of lead that made it unsafe to drink, ABC News reported.
The results were based on information provided by the Environmental Protection Agency. Other dangerous substances found in water supplies included arsenic and copper; many also contained dangerous bacteria.
"There's a two-tiered drinking water system in this nation and rural America is most at risk from the inequality," Mae Wu, a senior attorney with NRDC's Health and Environment Program, told ABC. "Small systems have the highest percentage of water violations, and it's largely due to financial and technical capacity issues that will only get worse when the EPA cuts drinking water programs."
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One of the most publicized instances of water contamination occurred in Flint, Michigan, where high lead levels were recorded.
An emergency was declared in January 2016 after city and state mismanagement caused the contamination, Huffington Post reported.
Former President Barack Obama traveled to Flint and publicly drank some water from the city's supply to demonstrate it was safe, USA Today reported.
According to the NRDC report, small systems providing water to fewer than 500 people "accounted for nearly 70 percent of all violations and a little over half of all health-based violations."
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Rural areas were most dramatically affected.
"It verifies concerns that we have been expressing for the last 10 years, which is that these rural American cities are just not able to fund their water infrastructure needs and they cannot afford to upgrade their systems, nor can they afford to meet existing federal law," civil engineer and Virginia Tech Professor Marc Edwards said.
The NRDC report urged the government to triple funding for improving water infrastructure.
"They are really on their own. You can't really trust that the existing law is being enforced," said Edwards. "People are being told their water is safe when it is not. It is like being in a third-world country, while living in a first-world country."
An EPA statement declared the agency would be taking action.
"Under new leadership, EPA has made clear it is getting back to its core mission, which includes protecting America's drinking water," a spokesman told ABC. "Unfortunately, this is an area in which the past administration failed, as we saw the devastating consequences of Flint, Michigan and East Chicago, Indiana. Administrator [Scott] Pruitt is committed to helping modernize our country's outdated water infrastructure in order to ensure we maintain safe drinking water for the more than 300 million people that depend on it daily."