DETROIT (AP) — Drinking water is being shut off at all Detroit public schools because the water in 16 of them was found to have high levels of lead or copper.

Superintendent Nikolai Vitti said Wednesday that he’s turning off water at all schools “out of an abundance of caution” while more tests are performed. Officials believe old fixtures, not the water source, may be to blame.

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Detroit Public Schools Community District has more than 100 buildings and serves more than 40,000 students. The new school year starts next week.

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The district operates independently from City Hall, but Vitti says he’s working with Mayor Mike Duggan on water quality issues.

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