Because it’s not just Flint. In the last two months, reports of dangerous lead levels—from a variety of sources—in other cities and states have arrived almost every week. In late January, residents of Sebring, Ohio, were told not to drink the water. In February, California’s Governor Jerry Brown asked the state legislature to allocate $176 million to speed the soil clean-up effort at thousands of homes near a former lead battery plant.

On March 3, the New York Times reported that the children of Cleveland, Ohio, have higher levels of lead than those in Flint. Various reports have revealed there are 19 municipalities in Pennsylvania where children have higher lead levels than in Flint. Just last week, thirty schools in Newark, New Jersey were found to have dangerous levels of lead in the water; bottled water had to be brought in.

No one should be surprised. Although the United States has made great strides in reducing childhood lead poisoning, we never finished the job. Like marathon runners who fail to cover the final miles, we have left lead in pipes and on walls where children live. As a result, we have left hundreds of thousands of children at risk.

Since ancient times, humans have been digging lead out of the ground and finding ways to make use of it. For nearly as long, we have known that lead is toxic. Unlike some metals that are beneficial in small amounts, lead only harms human health. In young children, whose brains are still developing, it does permanent damage, lowering kids’ IQs, their ability to pay attention, and their impulse control.

The history of lead poisoning is full of tension between the metal’s usefulness and its health effects. The Ancient Greeks called lead “deadly,” but put it in plumbing, kitchenware, and tank linings. In 1786, Benjamin Franklin described the “mischievous effect from lead” in printers who worked with it. In 1904, two Australian doctors first linked lead paint to childhood lead poisoning. Within fifteen years, twelve countries had banned lead paint from interior use. Meanwhile, in the United States, it was promoted as a high-quality product. Between 1910 and 1977, Americans put an estimated three million tons of lead on walls, toys and furniture. And at the start of the automotive era, a lead emerged as a solution to engine knock, and was added to gasoline even though workers making the lead additive sometimes died from exposure to it.

Finally, in the 1970s and 1980s, a handful of scientists and doctors battled to show how ubiquitous and dangerous lead really was. As a result of their work, the metal was taken out of food cans, paint, and gasoline. The subsequent 90 percent reduction in Americans’ average blood lead levels counts as one of the great public health victories of the 20^th century.

And yet, there are still millions of lead pipes, like those that leached lead into Flint’s water, in all fifty states. And according to the National Center for Healthy Housing, up to 35% of homes across the United States still contain lead paint, the primary source of poisoning because it flakes off into dirt or gets on floors and windowsills where children play.

More than 500,000 American children are at or above the lead warning level set by the Centers for Disease Control, currently five micrograms of lead per deciliter of blood (although the CDC notes that there is no proven safe level of lead in the body). Almost certainly, these numbers don’t capture the full problem, because only 10% of children nationally who should be tested actually are.

With sufficient political will, we could prevent lead poisoning. If sources of lead exposure are removed or made inaccessible, there is no lead poisoning. Fixing the water supply requires first managing water chemistry (in Flint, city managers failed to add anti-corrosive measures to the water.) Over the long-term, lead pipes can be located and removed, either all at once, as may well happen in Flint now, or one by one, in the course of sidewalk and road repair. In houses, lead is only a problem when it begins to deteriorate. It must be either covered up or safely removed. We know how to do both.

Expensive? Yes. But in Flint the government now has to find money to remove lead pipes, and they are going to have to spend millions more taking care of children who develop neurological problems because of the the tainted water.

If anything good comes of Flint’s tragedy, let it be that in this presidential election year Americans—starting with Congress—finally resolve to finish what we started and eliminate lead poisoning for good. Everywhere.

Lydia Denworth is a Brooklyn-based science writer and the author of Toxic Truth: A Scientist, A Doctor and the Battle over Lead (Beacon Press).