Recent water tests at elementary schools in Flint have found an increase in samples showing lead levels above the federal action limit.
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.
The overall results are encouraging because they meet federal guidelines for lead if treated like samples collected by municipal water systems, Krisztian said. Flint's water was contaminated with lead in 2014 and 2015, when officials began tapping river water that wasn't properly treated.
The city's chief public health adviser and director of public works are working with department representatives, public health officials and researchers to review the data, Flint Mayor Karen Weaver said.
"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.
Flint Community Schools haven't been using tap water since September 2015. State-funded bottled water will likely continue to be supplied until all lead and galvanized service lines have been replaced, Weaver said.
State officials are expected to conduct another round of testing this month. The department will then make recommendations for how the state can help Flint moving forward.