A recent round of tap water tests in Flint, Michigan showed an increase in the number of elementary schools with lead levels above the federal action limit.
Lead levels became an issue in 2014 when officials switched the city's drinking water source to the Flint River.
The Michigan Department of Environmental Quality determined that 28 samples tested in February were above 15 parts per billion of lead, the Flint Journal reported. That compares to 20 such samples in January.
The increase may be due to changes in testing conditions, such as the decision to collect samples before flushing lines, said George Krisztian, a department spokesman. Samples collected before flushing tend to have higher lead levels because the water has been in contact with the pipes longer.
Flint Mayor Karen Weaver said Flint Community Schools have been using bottled water since September 2015 and likely will continue to do so until all problematic service lines have been replaced.
“I am convinced that these test results prove additional work and investigation is needed to determine the source (or sources) of the lead, and what actions must be taken to address and resolve the problem, once and for all,” Weaver said.