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 Legionnaire's disease.
Demonstrators demand action from the GOP presidential candidates about the water crisis in Flint before the GOP presidential debate on March 3, 2016 in Detroit, Michigan
The social costs 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.
Here is a timeline of the events:
APRIL 2014: In an effort to save money, Flint began drawing its water from the Flint River instead of relying on water from Detroit.
The move was considered temporary while the city waited to connect to a new regional water system.
Residents immediately complained about the smell, taste and appearance of the water.
They also raised health concerns, reporting rashes, hair loss and other problems.
To save money, Flint began drawing its water from the Flint River (pictured) instead of Detroit's in 2014. Residents immediately complained about the smell and taste of the water
SUMMER 2014: Three boil-water advisories were issued in 22 days after positive tests for coliform bacteria.
OCTOBER 2014: A General Motors engine plant stopped using Flint water, saying it rusted parts.
JANUARY 2015: Flint sought an evaluation of its efforts to improve the water amid concerns that it contained potentially harmful levels of a disinfection byproduct.
Detroit offered to reconnect Flint to its water system. Flint insisted its water was safe.
JAN. 28 2015: Flint residents snapped up 200 cases of bottled water in 30 minutes in a giveaway program. More giveaways followed in ensuing months.
FEB. 3 2015: State officials pledged $2 million for Flint's troubled water system.
Flint residents snapped up 200