You have no real way of knowing if your town, your family, or your children face the kind of water contamination that exposed everyone in Flint, Michigan, to lead poisoning. Not because Flint is an outlier--it may, in fact, be the norm---but because no one has enough data to say for sure.

Five state and local officials in Flint face involuntary manslaughter charges for failing to alert the public to the looming health crisis there. Yet a recent Reuters report found 3,000 geographic areas in the US with lead poisoning rates twice that of Flint. But you would be hard-pressed to determine whether you lived in one of them because the United States lacks the data---and data collection requirements---needed to know for sure whether people are being poisoned by their drinking water. President Trump’s proposed cuts to the Environmental Protection Agency’s could make it even harder to know.

“The data gaps are so huge. It is abominable. We have a huge number of people in this country living completely in the dark,” says Eric Feigl-Ding, an epidemiologist at Harvard University’s Chan School of Public health and founder of the public health website ToxinAlert.org.

Some 170,000 public water systems provide water to Americans. The federal government regulates that water under laws like the Safe Water Drinking Act and the Lead and Copper Rule, but leaves it to states, utilities, and property owners to test that water and enforce the laws.

Yet the number of taps that must be tested remains woefully small. The rules require water systems serving at least 100,000 people, for instance, to test 100 taps every six months. The requirements decrease from there. Systems that serve, say, 90,000 people must test just 60 taps. Smaller systems, only five. And certain systems qualify for reduced testing. In some cases, that means testing once every nine years.

“Would you really rely on a sample of 100 people in New York or Boston?” says Feigl-Ding. “In no universe is that going to give you a statistically significant result. That’s just ludicrous.”

Lead is measured in parts per billion, or ppb. If more than 10 percent of a given system’s taps exceed 15 ppb (referred to as the “action level”) the system operator must inform the public of the risk and report the violation to the state, which reports it to the EPA. But some researchers worry that even that threshold is too high and creates a cycle in which water systems worry more about compliance than keeping people safe.

“The system detects violations. It’s not set up to be useful,” says Jeffrey Griffiths, professor of public health at Tufts University. “If you had nothing but lead going straight to your house, nobody would know that, because all that gets captured is there was a violation.”

Griffiths says something as simple as GPS technology could vastly improve the ability of ordinary citizens to monitor their own risk levels. The hurdle to establishing such a system at the national level is each state has the authority to address the problem---or not---as it sees fit. “There’s a common understanding around what water contamination is,” he says, “but the degree to which they are enforced or there’s real help from the state is completely variable.”

Private property owners have no obligation to test their taps, a situation that includes privately owned wells serving small towns across the country. That said, if private property owners do detect lead in their water systems, they must address it. That can quickly get expensive. For that reason, most property owners skip testing entirely, says Angel Hsu, director of the Data-driven Environmental Group at Yale University. (The same problem applies to lead paint, another common cause of childhood poisoning.)

“This problem demonstrates the need for a federal program to underwrite lead clean-up,” Hsu says. “Cash-strapped people and municipal governments do not have the resources necessary to remedy such a broad and persistent hazard.”