After Flint, Mich., switched from purchasing water via Detroit to sourcing locally from the Flint River, residents began noticing a change in water quality. One resident—Lee Anne Walters—suspected the water might be toxic, and had her water tested for lead. She brought samples to Marc Edwards, an environmental engineer at Virginia Polytechnic Institute and State University and a world-renowned expert on water treatment. He found lead levels in her tap water at 13,200 parts per billion; the U.S. Environmental Protection Agency sounds the alarm at 15 ppb. She subsequently discovered her three-year-old son had blood lead levels so high that he was considered lead poisoned. In fact, researchers estimated 4 percent of all Flint’s children five and under had elevated blood lead--a percentage almost double that seen before the switch to the Flint River water.

Edwards and a Virginia Tech team stepped in, forming the Flint Water Study and testing almost 300 homes. They repeatedly found unsafe lead levels in the drinking water. They discovered that if Flint had been using an anticorrosion agent like orthophosphate minerals to coat city pipes, the lead crisis may have been averted. (Watch a Scientific American video about Flint's lead pipe corrosion.) Furthermore, Edwards’s team uncovered the widespread use of lead testing practices that deviated from EPA protocol—Flint residents were encouraged to “pre-flush” the pipes before each lead test, which would decrease the amount of lead reading in the test sample.

Edwards spoke to Scientific American guest contributor Jayde Lovell about the science behind what went wrong.

[An edited transcript of the interview follows.]

What sequence of events put more lead into the drinking water in Flint?

It turns out it is very simple: they didn’t follow federal law. Federal law requires that you have a corrosion control plan; a plan to stop the water from eating up your most expensive infrastructure—your pipes—and contaminating the water. That was the minimum acceptable response under the law. [Adding orthophosphates] would have cost $100 a day.

Instead, because the corrosion inhibitor wasn’t there, plus the Flint River had higher chloride—eight times higher chloride. Chloride is corrosive—it’s road salt. The combination of not following the law, plus more corrosive water, triggered everything.

When we went into this in September, we thought maybe the preventative treatment would not have worked [as the chloride was so high]. So we did lab experiments that, somewhat to our surprise, showed that the preventative treatment—the orthophosphates—if they’d done it, it definitely would have worked in this case. We proved that by experimentation.

If the right treatment had been added, in your opinion do you think the Flint River was a suitable choice for drinking water?

It was. I know people have reservations but we tested the river before and after treatment for contaminants, and we found it was a very suitable water source. It met federal standards. It may not look as good as Lake Huron, obviously. But with the effective treatments they had, it would have been deemed a success.

Now there’s a local perception—which is correct—that the Flint River was kind of a dumping ground over the years for G[eneral] M[otors] and other companies. But it’s a river, it had been flushed out; it’s been flushed out for 25 years and there’s really no evidence we could find of harmful levels of contaminants in the water.

How did the Flint River concentrate so much salt?

Well there’s some level that’s present naturally but in the U.S. we’re currently contaminating our rivers with road salt. Every year in the U.S., we put 135 pounds of salt per person on the road. I did not know that until I started looking at this issue: Why is chloride so high in Flint River?

We’ve got other cities where they’ve got low lead, and then they went above this threshold and suddenly the lead started coming off their pipes. The preventative treatment worked, and now it’s not working. In those cities the chloride has been rising. Chloride levels in some U.S. rivers have doubled in the last 20 years.

What government agencies are responsible for testing the water, and what methods do they use?

There is a [lead testing] method that’s specified by the EPA, and that’s the method I prefer. But over the years water companies have added extra steps—all of which tend to make lead lower when you sample it than when you drink it.

So in Flint they were using some of these extra steps—a pre-flushing technique. So the irony is that even as National Guard people walk the streets and people are being told to use filters, Flint has never failed the [EPA’s] Lead and Copper Rule. I have been fighting for the last 10 years to try to just make the rule be followed.

Under the Lead and Copper Rule the water company only has to sample 100 homes once per year. The bargain was, “We won’t make you sample everyone’s house, but if you pick these 100 houses to be the worst houses, and you sample the worst houses, if there’s a problem we will see it.” That’s the logic. Then you’ll know if you have a problem.

Well, they’ve never done that. They tend to go sample 100 houses that don’t have lead. The EPA never enforced it’s own rule. That’s what was happening in Flint—Flint was telling the state, in writing, “Every house we sampled has a lead pipe.” That was all a lie. That’s been acknowledged now.

If residents are concerned, how they can test if their water is safe?

In recent years we’ve learned that simply testing the water one time doesn’t tell you much. The problem is coming from pieces of rust that fall off into the water at [random] intervals. Sometimes a chunk of that corrosion will fall off a lead pipe. If you’re unlucky and you put your glass under the tap at that time, you can drink a glass of water that creates the same lead exposure as eating eleven paint chips.

As long as you have lead pipes and lead plumbing, you have a hazard. I recommend buying a $20 lead filter, and if it’s NSF [National Sanitation Foundation]-certified, you put it on your tap and you can filter all the water you use for cooking or drinking. You can dramatically reduce or almost eliminate lead hazards in water used for cooking or drinking. They’re rated up to 125 ppb by the National Sanitation Foundation, but we’ve tested them at much higher levels, and they’re very effective.

What are you and your team doing now?

We do everything related to plumbing systems in big buildings, and the opportunistic infections like legionella. It’s been our niche area. After we started counting bodies of people dying of legionella, people started to take this very, very seriously—so that’s where we’ll be continuing our work.

I feel strongly that we’re defending science and engineering as a public good. I feel the stakes are incredibly high. If you’re waking up every day with a sense of purpose, there’s no stopping you. That’s how our team feels.