• Toxins used to stain-proof furniture and fight fire is in public water supply
• California worst affected, also New York, Florida, Georgia, and others
• At least 6m people affected, possibly more. Fed data omits 100m people
• The case echoes Flint, where 8,000 children were exposed to lead in water

More than six million people in the U.S. drink and use water that is contaminated with deadly toxins, a new study reveals.

Life-threatening concentrations of a human-made carcinogenic chemical - commonly used to fight the fire, insulate pipes, and stain-proof furniture - have been found in public water tanks across America.

The most at-risk states are (in order): California, New Jersey, North Carolina, Alabama, Florida, Pennsylvania, Ohio, New York, Georgia, Minnesota, Arizona, Massachusetts, and Illinois.

The Harvard University study, published on Tuesday, warns the figures are likely woeful underestimates since government data does not account for a third of the country - and therefore omits around 100 million people.

It comes amid the ongoing crisis in Flint, Michigan, over lead-poisoned water.

The scandal, which dates back to April 2014, sent shockwaves through the nation as many as 12,000 children were exposed to potentially life-threatening chemicals.

But this new study suggests a similar crisis could be much more widespread.

'For many years, chemicals with unknown toxicities, such as PFASs, were allowed to be used and released to the environment,' said lead author Xindi Hu, a doctoral student at Harvard's Chan School of Public Health.

'We now have to face severe consequences.'

The toxins found in the water supply are called polyfluoroalkyl and perfluoroalkyl substances. They are commonly known as PFASs.

PFASs have been used over the past 60 years in industrial and commercial products ranging from food wrappers to clothing to pots and pans.

They have been linked with cancer, hormone disruption, high cholesterol, and obesity.

The researchers looked at concentrations of six types of PFASs in drinking water supplies, using data from more than 36,000 water samples collected nationwide by the U.S. Environmental Protection Agency (EPA) from 2013-2015.

They also looked at industrial sites that manufacture or use PFASs; at military fire training sites and civilian airports where fire-fighting foam containing PFASs is used; and at wastewater treatment plants.

Safety officials have yet to find a way to remove PFASs from wastewater by standard treatment methods, so they easily contaminate the public supply.

The sludge that the plants generate - which is frequently used as fertilizer - could also contaminate public water.

The study found that PFASs were detectable at the minimum reporting levels required by the EPA in 194 out of 4,864 water supplies in 33 states across the U.S.

Drinking water from 13 states accounted for 75 percent of the detections, including, in order of frequency of detection, California, New Jersey, North Carolina, Alabama, Florida, Pennsylvania, Ohio, New York, Georgia, Minnesota, Arizona, Massachusetts, and Illinois.

Sixty-six of the public water supplies examined, serving six million people, had at least one water sample that measured at or above the EPA safety limit.

The limit is 70 parts of PFASs per trillion (ng/L).

Concentrations ranged as high as 1,800 ng/L for PFOS. That was in Newark, Delaware.

The highest levels of PFASs were detected in watersheds near industrial sites, military bases, and wastewater treatment plants--all places where these chemicals may be used or found.

'These compounds are potent immune toxicants in children, and recent work suggests drinking water safety levels should be much lower than the provisional guidelines established by EPA,' said Elsie Sunderland, senior author of the study and associate professor at the Harvard Chan School.

Although several major manufacturers have discontinued the use of some PFASs, the chemicals continue to persist in people and wildlife.

Drinking water is one of the main routes through which people can be exposed.

What are the Chemicals the Study Detected? 

The toxins found in the water supply are called polyfluoroalkyl and perfluoroalkyl substances. They are commonly known as PFASs.

PFASs have been used over the past 60 years in industrial and commercial products ranging from food wrappers to clothing to pots and pans.

They have been linked with cancer, hormone disruption, high cholesterol, and obesity. 

They are used at industrial sites, military fire training sites, civilian airports where fire-fighting foam is used, and at wastewater treatment plants.

Safety officials have yet to find a way to remove PFASs from wastewater by standard treatment methods. 

The sludge that the plants generate - which is frequently used as fertilizer - could also contaminate public water.

Echoes of Flint: As Study Find Toxics in Water Across America, A Look Back at Michigan's Lead Scandal

Authorities in the financially struggling city of Flint, Michigan, switched its water source from Detroit's system to the Flint River to save money in April 2014.

The river water was more corrosive than the Detroit system's and caused more lead to leach from Flint's aging pipes. 

Lead can be toxic, and children are especially vulnerable. 

Some 8,000 children are believed to have been exposed to lead poisoning since April 2014. And there has been an uptick in cases of Legionnaires disease.

The social costs are stemming from the scandal amount to $395 million, according to a recent analysis by a professor at the Columbia University Mailman School of Public Health. 

The crisis has prompted lawsuits by parents in Flint, which has a population of about 100,000, who say their children have shown dangerously high levels of lead in their blood.

In July, six state employees in Michigan were criminally charged in connection with the case. 

Some critics have called for high-ranking state officials, including Governor Rick Snyder, to be charged. Snyder said he believes he's done nothing criminally wrong.