Michigan’s attorney general has filed charges against three officials over contaminated water supplies in Flint.
Two state employees in the environmental department have been charged with misleading the US government about the problem.
And a Flint employee is being charged with altering water test results.
Nearly 100,000 residents of the poor, mostly black city, were exposed to high levels of lead, sparking an outcry.
Lead exposure can cause learning disabilities and behavioural problems in children.
“They had a duty to protect the health of families and citizens of Flint and they failed,” said Michigan Attorney General Bill Schuette.
He told reporters the three individuals would face a mixture of charges including tampering with evidence, conspiracy and misconduct in office.
The two state Department of Environmental Quality employees could face up to five years in jail.
The other man charged is a local water treatment supervisor.
Analysis: Michelle Fleury, BBC News
The crisis in Flint is about much more than clean water. It is about failed governance and accountability. And anger.
Melissa Mays told me in January how after a year of drinking contaminated water, her family began to lose their hair and developed painful rashes on their arms and face.
At the time, Flint residents were told it was okay to drink the water that was so corrosive that automaker General Motors stopped using it to clean its car parts.
Today’s charges represent a small step forward in finding out who is answerable for a health emergency in one of America’s most vulnerable cities.
But Michigan will have to do a lot more before Flint residents trust public officials again.
Governor Rick Snyder of Michigan has promised accountability for the decisions that led to the poisoning of Flint’s tap water. And he said this week he would drink filtered Flint water at home and at work for the next 30 days.
For Melissa Mays, though, it’s deja vu. She remembers the summer of 2015 when former Mayor Dayne Walling drank a mug of filtered water and told Flint residents how safe it was.
Mr Schuette said the charges were just the beginning of the investigation and more charges were expected with “nobody off limits”.
There have been calls for Michigan’s Republican Governor Rick Snyder to step down over the crisis.
Mr Snyder was grilled by Congress over his role in the crisis in March.
After the charges were announced, Mr Snyder called them “troubling” and said it “raises what happened to a whole new level”.
He said it is “critically important” the investigations continue.
The governor has also vowed to drink filtered water from Flint for 30 days to prove it is safe.
The water problems began in 2014 when the city switched its water supply away from Detroit’s water system, which draws from Lake Huron, and began to instead draw water from the Flint River.
The switch was meant to save the city millions of dollars.
But the water from the Flint River was more corrosive than Lake Huron’s water and the pipes began leeching lead.
Seven families have filed a lawsuit against Flint authorities.