DETROIT (Reuters) – Federal health officials on Friday confirmed that the blood lead levels of children in Flint, Michigan, rose after the city switched to the Flint River as the source of its drinking water, exposing residents to dangerously high contamination.

Flint, with a population of about 100,000, was under control of a state-appointed emergency manager in 2014 when it switched its water source to the river from Detroit’s municipal system to save money. The city switched back in October.

The river water was more corrosive than the Detroit system’s and caused more lead to leach from aging pipes.

Lead can be toxic, and children are especially vulnerable. The crisis has prompted lawsuits by parents who say their children have shown dangerously high levels of lead in their blood.

U.S. Centers for Disease Control and Prevention officials said on Friday that they found that the percentage of young children with elevated blood lead levels was significantly higher when the water source was the Flint River.

“This crisis was entirely preventable, and a startling reminder of the critical need to eliminate all sources of lead from our children’s environment,” Patrick Breysse, director of the agency’s National Center for Environmental Health, said in a statement.

When the water source was switched back to the Detroit system, the agency said, the percentage of children under 6 years old with elevated blood lead returned to levels seen before the switch.

The agency urged residents to use filters on their faucets to get water for drinking, cooking and brushing teeth. It said regular tap water could be used for bathing and showering because lead is not absorbed into the skin, but young children should not be allowed to drink bath water.

The U.S. Environmental Protection Agency said on Thursday that properly filtered water in Flint was safe to drink. City officials, however, said bottled water was still needed since not every home can use the filters.

(Reporting by Ben Klayman; Editing by Lisa Von Ahn)