Michigan's governor faced blistering criticism from US lawmakers Thursday over his role in the Flint water scandal that saw sky-high levels of toxic lead enter the city's water supply, but insisted he was not the only one to blame.

At a congressional hearing, Governor Rick Snyder -- flanked by the head of the federal Environmental Protection Agency, Gina McCarthy -- was grilled over the handling of the crisis. Both officials faced calls to step aside.

More than 8,000 children are believed to have ingested tainted water in economically devastated Flint, which saw lead levels soar for more than a year before citizen activists brought the tap water contamination into the public eye.

Snyder on Thursday accepted some responsibility for the debacle, but told the House Oversight Committee there was plenty of blame to go around, including at the federal and local level.

"Not a day or night goes by that this tragedy doesn't weigh on my mind -- the questions I should have asked, the answers I should have demanded, how I could have prevented this," Snyder told the House Oversight Committee.

He was adamant however that responsibility for the crisis was not his alone.

"Let me be blunt: This was a failure of government at all levels -- local, state, and federal officials. We all failed the families of Flint," he said at the hearing to uncover what went wrong in the city, and what steps are being taken to clean up the water supply.

The Michigan governor said his goal at this point was "delivering permanent, long-term solutions and the clean, safe drinking water that every Michigan citizen deserves."

- Tough questions -

McCarthy also faced a tough grilling -- mostly from Republican lawmakers -- over why it took a year for her agency to act, and why no one at the EPA has been fired so far, although one senior official has resigned.

Snyder's administration ordered various cost-cutting measures in financially struggling Flint -- including a shift in the water supply from the Detroit River to the Flint River.

That, as it turns out, was a grave error, Snyder now admits.

Experts believe that the chemical-laced Flint River water corroded lead-bearing pipes, allowing large amounts of the chemical element to leach into the city's water.

But Democrats on the panel did not accept the governor's apparent remorse.

"I'm not buying that you didn't know about any of this until October 2015," said Representative Matt Cartwright.

"You were not in a medically induced coma for a year," the Pennsylvania lawmaker said.

"I've had about enough of your false contrition and your phony apologies."

Critics who have called for Snyder's resignation say he dragged his feet for months after first learning of the problem, making a dire health emergency even worse.

"There's no evidence, even after you were warned by the mayor of Flint they had problems, and they begged you to come to Flint. You ignored them," said Representative Gerry Connolly of Virginia.

"I'm glad you're sorry now. I'm glad you're taking action now, but it's a little bit late for the kids in Flint whose health has been compromised, for people whose health and immunity systems were already compromised, for a city in America that is on its knees because of your emergency manager's decision to save four million dollars."

- Flint's future -

The crisis was a huge blow to Flint, a once-thriving Rust Belt city already struggling from years of car industry shutdowns and layoffs.

Snyder told lawmakers however that he took action soon after being alerted to the city's water problems.

"First, we quickly reconnected to the Detroit water supply to begin sealing the damaged pipes," he testified.

"Second, I ordered the immediate distribution of water filters and extensive blood-level testing in schools and homes to identify those at the highest risk so they received health care, nutrition and additional support," he said.

He added that additional diagnostic testing, home nurse visits and home water testing have been put in place.

The hearing was held on the same day that a news report found the problem of lead in US water supplies may be far bigger than previously known.

Some six million Americans have drinking water tainted with higher levels of lead than allowed by federal guidelines, USA Today reported on Thursday.

The newspaper launched an investigation which found higher than acceptable lead levels in about 2,000 water systems across the United States.

Tainted water was supplied to hundreds of day care centers and schools, the report said.

Children are the population most vulnerable to the pernicious effects of lead, a toxin which affects the neurological system and can lead to permanent learning delays and behavioral problems.