Toxic lead has been seeping into Chicago’s drinking water, and the city is dragging its feet to fix the problem, according to an analysis published Thursday by the Chicago Tribune.

Lead was found in 70 percent of the 2,797 homes the Tribune sampled across the city since January of 2016. And three in 10 of those had lead concentrations higher than 5 parts per billion (ppb), the Food and Drug Administration’s upper limit for lead in bottled water.

Since the lead crisis in Flint, Michigan, Chicago has distributed thousands of free lead-testing kits to its residents in an attempt to figure out how bad the problem was. But once the results started coming in, the city buried them: Chicago hadn’t updated the city-run website tracking the results of its own tests in more than six months — until the Tribune started asking questions.

“Chicago’s water consistently meets and exceeds the U.S. EPA’s standards for clean, high-quality drinking water,” Megan Vidis, a spokesperson for the city’s water department, told VICE News. “The Department of Water Management proactively uses corrosion-control measures to ensure that it stays that way.”

“We can't be held to standards that we're not held to,” Vidis added, referring to the Tribune’s using the FDA’s benchmark for lead levels in bottled water in its report. “We're a huge municipal water system.”

There’s no known safe level of lead in children's blood, according to the EPA and the Centers for Disease Control. Ingesting the metal can cause irreversible brain damage and learning disabilities. And children who regularly drink water with more than 5 ppb of lead content have been found to have lead levels in their blood, according to a recent study from EPA scientists.

Mayor Rahm Emanuel has put forward an ambitious plan to replace 880 miles of the city’s aging water mains. But the plan leaves the responsibility to replace lead service lines — the lines that connect the mains to Chicagoans' actual taps — up to homeowners. Until 1987, Chicago required that all service lines to single-family homes and small apartment buildings be made of lead pipe.

And rattling those lead service lines during the construction to replace the water mains can actually make the problem worse. Construction near the lead pipe can shake loose the protective coating on the pipes meant to keep lead from seeping into tap water.

Since 2011, when Emanuel took office as the city’s mayor, Chicago has borrowed more than $481 million for water projects, including $312 million to install new water mains, according to the Tribune. To replace the service lines will cost more.

Still, other cities are footing the bill to ensure that their residents’ water is lead-free. Boston, Denver, Detroit, Milwaukee, Philadelphia, Pittsburgh, and St. Paul are all requiring that any municipal construction projects replace lead service lines.