(Reuters) - Lead levels in Flint, Michigan’s drinking water, the focus of a public health crisis, have fallen below federal limits, state officials said on Tuesday, although they cautioned residents to keep using filtered water as the city’s old lead pipes are replaced.

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Tests showed lead levels in the city’s drinking water were 12 parts per billion (ppb) between July and December, below the federal limit of 15 ppb, Michigan officials said in a statement.

The water crisis erupted when tests in 2015 found high amounts of lead in blood samples taken from children in Flint, a predominantly black city of about 100,000.

Flint was under the control of a state-appointed emergency manager when it switched its water source to the Flint River from Lake Huron in April 2014. The more corrosive river water caused lead to leach from pipes and into the drinking water.

Lead poisoning stunts children’s cognitive development, and no level of exposure is considered safe. Flint’s contamination prompted dozens of lawsuits and criminal charges against former government officials.

The city switched back to the previous water system in October 2015.

Flint’s lead levels are now comparable to levels in cities of similar size and with infrastructure of similar age, Michigan Governor Rick Snyder said in a statement.

Even with the test results, programs that provide water filters and related services will continue, he said.

“This is not the end of our work in Flint, but it is one more step along the path toward Flint’s future,” said Snyder, a Republican who has been sharply criticized by residents for his handling of the crisis.

Flint’s mayor, Karen Weaver, said in a statement she would continue efforts to replace the estimated 20,000 lead-tainted pipes that remain in the city.

“We are not out of the woods yet. My goal has not changed. All of the lead-tainted pipes in Flint still need to be replaced,” she said.

Flint resident Melissa Mays, a plaintiff in a drinking water lawsuit, said the results were misleading because only one-third of Flint homes had been tested and the state had not identified which homes have lead pipes.

“Until they get every home to test zero, they should not be making these statements,” she said. “It’s giving residents a false sense of security.”

In December, Michigan Attorney General Bill Schuette charged four former officials with conspiring to violate safety rules, bringing to 13 the number of current and former officials charged in connection with the crisis.