The trouble with trying to solve the country’s lead problem is that all the easy fixes have already been done. “Yes, if we could replace all of our 100-year-old water mains overnight, we’d gladly do it,” says Gary Burlingame of the Philadelphia water department. But such projects can carry a steep political and economic price tag. Here’s what it would cost to put a dent in the lead exposure of American kids:

$1 trillion

To make all U.S. pipe replacements deemed “urgent” by the American Society of Civil Engineers

$216 billion

To perform lead-paint abatement on the 24 million at-risk homes, at an average cost of $9,000 per home

$3 billion

To treat the estimated 535,000 children with injurious levels of lead in their blood

$18 million

To test the soil in the 13,500 playgrounds in the 100 largest U.S. cities

A version of this article appears in the March 1, 2016 issue of Fortune.