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The House Oversight and Government Reform Committee is holding a high-profile hearing Wednesday about the Flint water crisis. Below, your guide to what the hell is going on.

What is wrong with the water in Flint, Michigan?

There’s too much lead in it, and exposure to lead can cause irreversible neurological damage to infants and children.

How did the lead get in the water?

The city began using the Flint River as a water source in April 2014. Flint had previously used water from Lake Huron that was treated in Detroit. The water from the Flint River was much more corrosive than the water that had been piped in from Detroit, and it caused lead found in plumbing materials to leach into tap water.

Why did the city switch to the Flint River in the first place?

To save money. Officials wanted to connect Flint to a new Lake Huron pipeline, which would save the city $4 million dollars a year. But it was going to take two years for that pipeline to be ready, so the Flint River was chosen as Flint’s water source in the meantime—and water from the river was processed at Flint’s treatment plant, which had previously only been used as an emergency backup.

Why was the Flint River so corrosive?

Because of its high chloride content. Per UC–Berkeley water expert Tim Pine, rivers can be high in chloride because of salt that drains into them from sources “both natural (leaching from soils) and man-made (road de-icing, airports, feedlots, and farming).”

Do other cities’ drinking water sources have that problem?

Yes—but other cities, like Detroit, that are concerned about possible corrosion treat their water with a substance called orthophosphate. Flint did not do this. (It’s possible, though, that the Flint River’s chloride levels are so high that even orthophosphate wouldn’t have helped.)

How widespread is the lead contamination?

Not all plumbing materials are made of lead, so levels can vary from neighborhood to neighborhood and home to home, and the complete results of a large-scale federal survey of thousands of Flint homes haven’t been released yet. But a team from Virginia Tech, assisted by residents themselves, did sample 252 homes in a study released in September 2015. The results of that study take some explaining, but it’s the most complete look available at the scope of the problem:

• The Safe Drinking Water Act’s Lead and Copper Rule says lead levels are unacceptable if the 90^th percentile value of a set of lead measurements in homes that are at high risk of contamination is 15 parts per billion or higher. (Homes are at high risk if they contain or are served by plumbing materials in which lead is used.) The Virginia Tech team found a 90^th percentile value of 25 ppb in the samples it collected and found an average level of contamination of 10.6 ppb. Sixteen percent of the homes tested were above 15 ppb.
• A 2014 medical study cited by the Virginia Tech team found that 25 percent of infants drinking formula made from 10 ppb tap water would develop lead-in-blood levels considered “elevated” by the Centers for Disease Control and Prevention.
• The Virginia Tech tests were distributed to residents by a local activist group; neither the group nor the Virginia Tech team had access to data that would have helped it target high-risk homes.

In other words, an untargeted study found lead levels well over what the Environmental Protection Agency would consider dangerous in targeted high-risk areas—and found an average contamination level that, according to another study, would cause what the CDC defines as “elevated” lead levels in 1 out of 4 infants.

An official from the United States Public Health Services, meanwhile, recently told the New York Times that it had measured lead levels of 150 ppb or higher in 26 Flint water samples, which is a level at which even the water filters that have been distributed to residents can’t make the water safe to drink. Tap water in the home of a Flint woman named LeeAnne Walters has measured as high as 13,200 ppb.

How many children are going to be sick because of this?

The CDC defines an elevated blood lead level as 5 micrograms of lead in a deciliter of blood. A study released in September 2015 by Flint’s Hurley Medical Center found that the number of children 5 years and younger meeting that threshold had doubled since the city’s switch to the Flint River as a source of drinking water, and Michigan Gov. Rick Snyder said recently that a total of 200 cases of elevated levels have been documented since last fall.

But without data on each Flint home’s lead levels, it’s hard to say how many kids might have been ultimately exposed, and individuals’ blood lead levels recede quickly, so you can’t just go and measure every child in Flint at this point and know who might have been affected going back to April 2014.

What does lead do to kids?

Lead exposure in young children is associated with neurological damage like reductions in IQ and attention-deficit problems even at levels less than 5 micrograms per deciliter. There is no level of lead exposure greater than zero that is considered conclusively safe by public health authorities.

Does lead poisoning cause problems for adults?

Adults are not as vulnerable as young children to lead-related brain and nervous-system damage, but blood-lead levels of 40 micrograms per deciliter in adults have been associated with “neurotoxic effects” and cardiovascular problems. The EPA also considers lead a “probable human carcinogen.”

Was there anything else in the water besides lead?

Yes, actually. Other dangerous substances and organisms that have been found in Flint water since the April 2014 switch include total coliform bacteria, Legionella (the bacteria that causes Legionnaires’ disease), and substances called total trihalomethanes, which the EPA cites as potential carcinogens. You may also have seen pictures of Flint residents holding up jugs of yellow water; that discoloration is the result of excessive iron, which can also be harmful because it counteracts the chlorine (not chloride, chlorine) that is put in water to kill pathogens. At this point the most thoroughly documented problems in Flint involve lead, but anecdotally many adult residents have reported that using their tap water has caused rashes and hair loss, which would suggest other widespread issues as well.

Is Flint still using the Flint River?

No. The city switched back to water from Lake Huron (supplied once again via Detroit) in October 2015. But the corrosion was substantial enough that there are still dangerous amounts of lead in some of Flint’s tap water. It’s not clear how long it will take until the water is clean.

Who is responsible for all of this?

The short answer? Everyone. Rick Snyder appointed the “emergency managers” who approved and implemented the city’s decision to switch to using the Flint River and who refused to reconsider the decision when residents began complaining about the new water. The city of Flint’s employees failed to properly vet the Flint River as a water source and failed to treat the new water adequately. The Michigan Department of Environmental Quality—run by a Snyder appointee—should have required Flint to have a “corrosion control” plan in place before the switch but failed to do so because, it says, it misinterpreted a rule. After the switch was made and residents began complaining about the appearance, smell, and seeming unhealthiness of the water, the MDEQ said Flint was passing all required quality tests (in retrospect a dubious claim) and supervised flawed sampling studies (which were perhaps flawed on purpose) conducted by Flint employees that erroneously concluded that the water was still safe. The Michigan Department of Health and Human Services appears to have noticed in July 2015 that lead levels were unusually high in Flint children but then done nothing with that data.

On the federal level, an EPA employee named Miguel Del Toral wrote an internal memo in June 2015 outlining concerns about Flint’s water. His memo, which became public when Flint resident LeeAnne Walters gave a copy of it to an investigative reporter at the Michigan American Civil Liberties Union, turns out to have been completely prescient. But at the time, the EPA publicly nay-sayed it as a set of “initial results” that others would have to “verify and assess,” and did not require Flint to take any action to improve water treatment.

Michigan officials also made a variety of public statements about the crisis that now seem dangerously unjustified. In July 2015, MDEQ spokesman Brad Wurfel (who has since resigned) said that “anyone who is concerned about lead in the drinking water in Flint can relax.” In September 2015 Wurfel called Miguel Del Toral a “rogue employee.” And in that same month Rick Snyder’s spokeswoman—Sara Wurfel, who is married to Brad Wurfel!—said that the Hurley Medical Center study of lead exposure was “spliced and diced” to exaggerate Flint’s problems. (She has since left the Snyder administration for the private sector.)

Basically almost everyone at a city, state, and federal level who had responsibility for Flint’s water quality—whether that responsibility was assigned to them by law or just by their job description—failed.

So Flint just went ahead and switched to using water from a river in an area of the country infamous for industrial pollution without doing anything to check to make sure it wasn’t poisoned?

Yes, that seems to be what happened. When Flint piped its water in from Detroit, the Flint treatment plant was only used for backup purposes and was only operated four times a year. It’s not clear whether Flint water department employees even considered the possibility of major corrosion and lead leaching before the switch was made.

Why do we use lead in plumbing equipment if it’s poison, by the way?

Per Upmanu Lall, the director of the Columbia Water Center at Columbia University, “lead is exceptionally malleable, resists small leaks and can be shaped easily, so it was commonly used for plumbing for a long time.” It wasn’t until 1986 that research into lead’s health effects led to a ban on its use in new plumbing materials, and it’s still present in many houses and in water-system infrastructure built before that time.

So who finally figured out what was going on? Just Del Toral and Virginia Tech?

If there’s a single hero in Flint, it’s LeeAnne Walters, the resident whose tap water has been found to contain stratospheric levels of lead. Walters personally contacted Del Toral and through his suggestion got in touch with Marc Edwards, who led the team from Virginia Tech. The objective data in the reports by Del Toral, Edwards, and Dr. Mona Hanna-Attisha of the Hurley Medical Center seems to have created the tipping point that convinced public officials to act and turned Flint into a major national story.* National publications like Slate then piggybacked on the excellent reporting done by outlets like MLive, Michigan Radio, and the Michigan ACLU, which had been covering the story since the Flint River switch was made.

But ultimately it’s Flint residents like Walters—the people who began showing up to community meetings to complain about the water almost as soon as the switch happened and who helped the Virginia Tech team by supplying samples of their own water—who got everyone else to finally pay attention and do something.

Has anything similar to this ever happened anywhere else in the U.S.?

Marc Edwards was actually involved in exposing a similar crisis in Washington, D.C., where tests began discovering widespread lead leaching—which was then downplayed by public authorities who only admitted the extent of the problem under heavy pressure from activists and experts—about 15 years ago.

Have any of the responsible parties named above lost their dang jobs?

The head of the MDEQ and the aforementioned MDEQ spokesman have resigned, as has the regional EPA administrator who was responsible for Michigan. Before the crisis became a major story, the emergency manager who implemented the Flint River switch, Darnell Earley, had left Flint and was appointed by Snyder to a similar job with the Detroit school system. His tenure there was also controversial, and it was announced on Tuesday that he is stepping down from that position as well.

Why did Flint have an “emergency manager” in the first place?

Because of a controversial Michigan law that allows the governor to supersede local elected officials by appointing someone to take complete control of cities in financial crisis. The cities that have been affected by the law have had disproportionately black populations—57 percent of Flint’s residents are black, for example—and some argue that it’s essentially a tool of disenfranchisement.

Speaking of the governor, what’s going to happen to him?

Whether there will be personal fallout for Rick Snyder is an open question. Michigan attorney general Bill Schuette announced an “independent” inquiry into the Flint crisis and Wednesday’s congressional hearings might lead to further investigation. But the Michigan inquiry is being led by a prosecutor who personally donated thousands of dollars to Schuette’s and Snyder’s campaigns, while the congressional hearing is controlled by Republicans who denied a Michigan representative’s request to call Snyder, also a Republican, to testify. For what it’s worth, the Detroit Free Press reports that Snyder has an approval rating of only 39 percent but that only 29 percent of Michigan residents believe he should resign.

The federal Justice Department has also said it’s investigating the Flint crisis, which could lead to criminal charges or a civil suit being filed, but there’s been no suggestion that Snyder would be targeted by such actions.

Is it possible Snyder covered up evidence that the water was bad?

The state government was certainly not proactive about investigating residents’ complaints about water problems, and the MDEQ and MDHHS seem to have ignored statistical indications of danger in summer 2015. But there’s no evidence that Snyder was personally involved in those failings.

Is anyone getting sued?

A number of class-action lawsuits have already been filed against city and state organizations and officials on behalf of Flint residents. It could be difficult for plaintiffs in these lawsuits to win money because governments and officeholders are typically immune from paying damages. But it’s possible that the plaintiffs will overcome the immunity problems with creative legal arguments and/or seek damages in the form of material water-system repairs.

What else is being done to fix the mess?

For the last month-plus, the Michigan National Guard, state police, and many volunteers have been distributing water testing kits, water filters (which don’t work on the most tainted water), and bottled water (which has been donated en masse by charities and celebrities) to residents. (A state police official told ABC that the state has both the capacity and the need for further bottled water donations.) The state has allocated $28 million for medical assessments and nurses’ visits for potentially lead-exposed children. The Obama administration has specifically linked an allocation of $80 million for Michigan infrastructure projects to the Flint crisis. And congressional representatives are seeking further funding to repair or replace all of Flint’s lead plumbing—a project that they say will cost $800 million. (Recall that the city switched to Flint River water in the hopes of ultimately saving $4 million a year.)

Are there any crucial questions about the Flint crisis that haven’t yet been answered?

Yes, here are a few:

• Whose idea was it to switch to Flint River water? We know that a Snyder-appointed emergency manager formally approved the move and that a Snyder-appointed manager implemented it. But who was responsible for advocating for the switch? And how far up the chain did the state’s botched Flint decisions go?
• Why didn’t anyone in the Flint water department prepare for the possibility that the Flint River water would be corrosive and contaminated with pathogens?
• Were the summer 2015 city/state tests that erroneously found that everything was fine flawed because of incompetence or because of a coordinated cover-up? And why didn’t the Michigan DHHS do anything when it found evidence of elevated blood levels in July 2015?

What about how all of this incompetence and negligence will ultimately impact the well-being of all 8,657 of Flint’s children under the age of 6?

That’s the biggest question of all—and one that Flint will be answering for decades.

*Correction, Feb. 3, 2016: This post originally misspelled Dr. Mona Hanna-Attisha’s last name.