Three Memphis schools in the Achievement School District have joined a growing list of buildings with water sources that contain unsafe lead levels, but the vast majority of schools in the district have yet to be tested.

One source at Frayser-Corning Achievement Elementary school had six times the state’s threshold for safe water, which is 20 parts of lead per billion parts of water. In addition, one source at Georgian Hills Achievement Elementary, and three sources at Whitney Achievement Elementary tested higher than the threshold. A water source could be a water fountain or a sink.

For children, ingesting even low levels of lead can interfere with brain development, cause aggressiveness or inattentiveness, and impede academic achievement, according to the U.S. Environmental Protection Agency.

So far, the three schools in the achievement district are the only ones that have reported testing results to the state environment and conservation department. The three elementary schools are run by the state education department as part of the Achievement School District, Tennessee’s turnaround district for struggling schools.

But 26 schools in the district run by independent charter school organizations also have to complete testing, and state education officials encouraged them to test over the upcoming winter break.

For its three direct-run elementary schools, the state education department decided to replace any water source that tested higher than 5 parts of lead per billion parts of water – 20 sources across the three campuses.

“The department has gone above and beyond the minimum requirements to remedy the issue,” said spokeswoman Morgan Taylor, adding that the department also distributed more than 3,000 bottles of water to supply the schools until the water sources were replaced.

Renee Smith, who had grandchildren in the state-run district, said although she was encouraged the state had replaced more water sources than required, she was also concerned that most schools in the district had yet to be tested.

“Those schools are so old, I don’t understand why this is a surprise that lead is in them,” said Smith, who also works for parent advocacy group Memphis Lift. “This should have been fixed years ago. Passing out hundreds of water bottles to the children so they can drink without hurting their bodies, come on now. It’s so sad.”

The first round of results from the achievement district comes after Shelby County Schools reported 39 of its buildings had water sources with high levels of lead, representing about 2% of water sources in the district’s 165 school buildings and facilities.

Related: Lead isn’t just in water or in schools. Here’s a look beyond the 39 Memphis schools with high levels of lead.

Students and staff in Shelby County Schools have the option of free, in-school blood testing provided by the county’s health department to determine if any have 5 micrograms of lead per deciliter of blood or higher — the level of concern for federal agencies.

But that testing option is not currently available for Memphis students in the achievement district, said Joan Carr, spokeswoman for the Shelby County Health Department.

Related: What parents need to know and do if their child’s school had unsafe lead levels in water tests

So far, more than 100 schools in 31 districts across Tennessee found at least one water source above 20 parts per billion.

The testing was prompted by a new state law requiring districts to test all water sources for lead and remove them if they have more than 20 parts of lead per billion parts of water.