When public school students in Detroit return to their classrooms next week for the first day of the school year, the water fountains will be dry.

Since 2016, water testing in the district has found elevated levels of lead or copper in dozens of schools. And while it is unclear how many of the district’s 106 schools currently have water quality issues, the drinking water will be turned off in all of them, Superintendent Nikolai P. Vitti said on Wednesday.

The latest round of water quality tests was conducted this year, and the results for 24 schools came in last week. Of those, 16 had at least one water source with elevated levels of lead, copper or both. That, coupled with testing results from 2016, brought the total number of schools with known water issues to 34.

It could take one more month for all of the schools’ test results to come back, Dr. Vitti said. He decided not to wait.