Claire McClinton, a GM retiree, said her house began to smell like garbage. Another resident, Bethany Hazard, says her water started coming out of the faucet brown and smelling like a sewer, and when she called the city to complain, she was told the water was fine.

The water was not fine. First, tests showed there was fecal coliform bacteria in the water, and the city had to issue numerous boil advisories to citizens. In response, engineers upped the amount of chlorine in its water, leading to dangerously high levels of trihalomethanes, or TTHMs, which put Flint in violation of the Clean Water Act. TTHMs are especially dangerous when inhaled, making showering in hot water toxic.

By October, GM, which still has a plant in Flint, had started noticing that the water was corroding parts of its engines. The plant switched off the Flint water, and started trucking in water from elsewhere. It asked the city for permission to use water from Flint Township, rather than the city of Flint (Flint Township was still buying water from Detroit), and switched back to Detroit water, said spokesman Tom Wickham.

LeeAnne Walters didn’t notice any changes right away. But a few months after the switch, she noticed that her children were getting rashes between their fingers, on their shins, on the back of their knees. Her four-year-old son, who has a compromised immune system, started breaking out into scaly rashes whenever he swam in their salt-water pool, which he’d used since birth. Then Walters’ 14-year-old son got extremely sick and missed a month of school.

So she sent her water off to Marc Edwards, a Virginia Tech environmental engineering professor who had forced the CDC to admit it had misled the public about the amount of lead in D.C.’s water.

Edwards was shocked when he found that Walters’ lead content was 13,000 parts per billion. The EPA recommends keeping lead content below 15 parts per billion.

“At first I didn’t believe the results because they were the worst I’d ever seen, and I’ve seen a lot,” Edwards told me.

None of the samples Walters sent were safe to drink. Some had lead content of 200 parts per billion. Over 30 samples, the average lead content was 2,000 parts per billion, which meant that no matter how long Walters let her taps run, it still would have been toxic. This could easily have been causing the health problems that Walters and her children were experiencing.

“Lead is the best known neurotoxin, it adversely impacts every system in the human body,” Edwards told me. “Certainly it could have caused children’s lead poisoning.”

The city says it does not know why so much lead was found in Walters’ pipes, but Edwards has a theory: Many cities have lead pipes, and when water sits in those pipes, the lead can leech into the water. So cities usually add corrosion-control chemicals, such as phosphates, to keep the lead out of the water. But because Flint didn’t take such precautions when they began pumping their own water, “the public health protection was gone,” Edwards says.