Corroded lead pipes which have been contaminating the tap water of Flint, Michigan must be replaced, says a lawsuit filed Wednesday, as the US state's embattled governor tried to contain the scandal.

Governor Rick Snyder vowed to help "address the damage that's been done" in the predominantly poor and black city of 100,000 after cost-cutting efforts exposed residents to lead poisoning.

But he stopped short of promising to replace the pipes, which began releasing lead after Flint switched to a cheaper but dangerously corrosive water supply.

Officials are accused of ignoring months of health warnings about foul-smelling and discolored water, even as residents complained it was making them sick.

"It's a lot of work to take out pipes, to redo the infrastructure," Snyder told reporters.

"The short-term solution is to hopefully recoat, and have it validated by third parties so we know the water is safely coming out."

Lead exposure is harmful to everyone, but it can have devastating impacts on young children by irreversibly harming brain development. It has been shown to lower intelligence, stunt growth and lead to aggressive and anti-social behavior.

Water treatment plants across the country are required to closely monitor lead levels in tap water and use chemicals to reduce acidity and coat pipes to prevent corrosion.

Snyder appointed a team of outside experts Wednesday to help the state resolve Flint's water crisis and deal with the long-term health impacts.

The state is also working to map out exactly where the old lead pipes are in Flint so it can "come up with the proper priorities about how we replace that infrastructure," Snyder said. However, he said that is a long-term project and declined to comment on the lawsuit.

Flint's mayor has estimated that the cost of fixing the damage done to the city's infrastructure by the corrosive water could reach as high as $1.5 billion.

The cash-strapped city was reportedly hoping to save $5 million over two years by drawing water from the Flint River beginning in April 2014 rather than continuing to buy it from nearby Detroit.

The state's environment department approved the switch even though the city's treatment plant was not able to produce water that met state and federal standards.

It cost $12 million to switch Flint back to the Detroit water system in October after a local pediatrician released a study showing that the number of children with elevated blood-lead levels had doubled from 2.1 to four percent.

Activists and environmentalists said the government needs to spend whatever it takes to make sure the water is safe to drink -- and complies with federal rules.

"For years the state told us we were crazy, that our water was safe, which wasn't true," said Melissa Mays of Water You Fighting For, a Flint-based organization which joined the American Civil Liberties Union and the Natural Resources Defense Council in filing the lawsuit.

"For the sake of my kids and the people of Flint, we need a federal court to fix Flint's water problems because these city and state agencies failed us on their own."