The water in Flint, Michigan, poisoned the town's children with lead for months. Michigan Gov. Rick Snyder has declared a state of emergency, which is necessary to get federal assistance to manage the problem.

Four percent of Flint's children have elevated levels of lead in their bloodstream — double the share affected a few years ago, according to tests from Flint's Hurley Medical Center confirmed by the state.

This all came about because a struggling Rust Belt city, trying to save money while under emergency management, ended up failing at one of its most basic tasks: providing safe drinking water. And the problem was compounded by ignoring months of warnings from activists who felt Flint's water was not safe to drink.

The decision, and the state's insufficient water testing, led to irreparable damage. There's no amount of lead safe for children to drink, and the effects of lead poisoning last a lifetime.

How Flint poisoned its children while trying to avoid bankruptcy

The lead crisis in Flint has been public since October and suspected long before that. But things were bad in the Michigan city long before its tap water turned out to be unsafe.

Flint was once a prosperous manufacturing town, but it never recovered from the closure of General Motors plants in the late 20th century. By 2013, when the water saga started, Flint's population had dropped from 200,000 in the city's heyday in the 1960s and 1970s to about 99,000 today. Its landscape was dotted with abandoned homes. The unemployment rate was 16 percent. Forty-two percent of residents, including two-thirds of children, were living in poverty — a higher share than even Detroit, which had become a symbol of post-recession urban blight.

Flint was also going broke. It had lost 75 percent of its property tax base since the 1980s. In 2011, an emergency manager took control of the town's finances. The city was overloaded with $1.1 billion in unfunded pension costs.

There wasn't much left to cut: Budget cuts had already slashed Flint's police force, cutting the total number of officers from 265 in 2007 to 122 in 2012. In 2013, it was named the most dangerous city in America.

So Flint, under the control of a state-appointed emergency manager, decided to save money on water. It had been purchasing water from Detroit, but costs had been climbing even as Flint's population fell. In 2013, the city decided to join a new, regional water system that, like Detroit, drew water from Lake Huron. The switch would save millions of dollars per year.

The problem was that the regional water system wasn't yet built, and Flint wanted to start getting its water from somewhere other than Detroit right away.

So the city started taking its water directly from the Flint River in 2014 — celebrating its break from Detroit with a countdown and a toast, Michigan Radio reported.

Who is responsible for this decision is a point of contentious political debate. The city council voted to switch to the new water system. But the decision to use the river instead was never brought to a vote.

The state's former treasurer, Andrew Dillon, signed off on the switch, and Dennis Muchmore, Snyder's chief of staff, wrote in an email to the governor that the decision was ultimately Dillon's.

The order to put the river water treatment plant into operation was signed by one of the state-appointed emergency managers, Ed Kurtz, according to reporting from MLive. Another emergency manager, Darnell Earley, was in charge when the switch actually occurred.

Residents started complaining about the water's smell and taste almost immediately, saying it caused rashes, hair loss, and other health problems. A nearby General Motors plant said the water was damaging its car parts and quit using it. At one point, residents had to boil water due to bacteria.

But the city assured them that everything was fine, and that the bad smell and taste didn't necessarily indicate other problems. They claimed federal tests showed the water was safe.

Flint officials took a very long time to admit they had a lead problem

Even as other problems with Flint's water were uncovered — bacterial contamination, as well as high levels of other contaminants that can cause liver problems — the lead poisoning remained hidden.

In late June, an employee at the US Environmental Protection Agency's Chicago office leaked a report on Flint's water to a local activist, whose son had developed a rash after swimming in a pool filled with Flint water and was diagnosed with lead poisoning. It said tests found high lead levels in the water. The city had told the woman the lead came from her plumbing, not the water.

But Flint continued to deny it, saying the report was released prematurely by a "rogue employee." Flint's lead problem wasn't made public until early fall, after outside researchers from Virginia Tech got involved and found extremely high levels of lead in the water of some Flint homes — and elevated levels in 40 percent of the homes the researchers tested.

In September, pediatricians reported that when the city bought water from Detroit, 2.5 percent of children under 5 in the most affected zip codes had elevated levels of lead in their blood. After the switch, that share had more than doubled, to 6.3 percent.

In the city as a whole, the proportion of children with high blood lead levels doubled, from 2.1 percent to 4 percent.

The state finally admitted Flint had a serious problem. In October, Flint began handing out water filters and began buying water from Detroit again, at a cost of $12 million.

The state Department of Environmental Quality admitted it had made a mistake in testing Flint's water for lead and other contaminants. "The water testing steps followed would have been correct for a city less than 50,000 people, but not for a city of nearly 100,000," Dan Wyant, the department's director, said in a statement.

Lead poisoning lasts a lifetime

Lead poisoning affects brain development so much that the gradual reduction of lead poisoning in American society has worked something of a miracle. Exposure to lead — and no amount of exposure is now considered safe — can lead to learning disabilities, lower IQs, and impulsivity. Those effects, multiplied over a city or state or country, are costly.

Eliminating lead in gasoline, Mother Jones's Kevin Drum argued in 2013, might be responsible for the dramatic drop in crime in the US in the 1990s:

If you add a lag time of 23 years, lead emissions from automobiles explain 90 percent of the variation in violent crime in America. Toddlers who ingested high levels of lead in the '40s and '50s really were more likely to become violent criminals in the '60s, '70s, and '80s.

But lead poisoning is still around, particularly in poor neighborhoods, where it's more likely to linger in paint on the walls of older houses. Freddie Gray, whose death in police custody led to protests in Baltimore last year, grew up around lead paint chips. Gray, like other Baltimore residents, won a settlement in 2010 from the landlords who allowed those conditions to persist.

In Flint, attorneys are recruiting plaintiffs for a class-action lawsuit against the city and state. It's likely to be a long process, but the damages from the city's brief stint of filtering its own water will last years.

Go deeper:

Kevin Drum's Mother Jones article on how lead poisoning caused the rise and fall of crime in the US is a testament to just how bad the condition can be.

Michigan Radio is in the middle of publishing a multipart documentary on Flint's water crisis that lays out the story in fascinating, horrifying detail.

Another horrifying lead paint scandal: An experiment in Baltimore in the early 1990s deliberately exposed children to lead in order to test the effectiveness of lead removal techniques.