The U.S. Environmental Protection Agency must strengthen its oversight of state drinking water systems in the wake of the lead crisis in Flint, Michigan.
The EPA's Office of Inspector General said in a report released Thursday that slow response from the agency exposed residents to lead-tainted water for far too long.
Flint's water was tainted for at least 18 months after the city switched its water supply from the Detroit water system to the Flint River as a cost-cutting measure.
The city switched its water supply in 2014 without ensuring that water from the Flint River had been treated with anti-corrosive agents, as required by law. It corroded the city's old water mains, turning drinking water brown because of iron contamination, and leached lead from smaller pipes that carried water into homes.
The report blamed not only the EPA but also state authorities who for months ignored complaints from Flint residents about the water.
But the report placed most of the blame on the EPA for not acting more quickly to make sure that state and local authorities were complying with the Safe Drinking Water Act, as well as with federal rules that mandate testing for lead.
In all, nearly 100,000 people were affected by the contaminated water, and U.S. federal health officials found that young children in Flint had significantly higher levels of dangerous lead in their blood.
Lead in water supplies can cause profound and permanent health problems, particularly in children whose brains and nervous systems are still developing.
The city returned to its original water source in October 2015.