(Reuters) - Detroit authorities on Wednesday ordered drinking water shut off at all city public schools after elevated levels of lead and copper were found in water at more than a dozen buildings with antiquated plumbing systems.

FILE PHOTO: Running tap water is seen in Michigan, U.S., May 4, 2016. REUTERS/Carlos Barria/File Photo

Over the weekend, supplies were cut at 16 schools and bottled water was provided until water coolers arrive, Detroit Public Schools Community District Superintendent Nikolai Vitti said.

Although there is no evidence of excessive levels of copper or lead in other schools, Vitti decided to shut off water throughout the system “until a deeper and broader analysis can be conducted to determine the long-term solutions for all schools,” he said in a statement.

“We have no reason to believe that any children have been harmed,” said Chrystal Wilson, a spokeswoman for the district.

About 50,000 students are enrolled in the district, which operates 110 schools, according to its website. Detroit public schools students are due to start classes on Tuesday, although teachers are already working.

The Great Lakes Water Authority and Detroit Water and Sewerage Department said in a statement that the water, after treatment, surpassed all federal and state standards for quality and safety. They attributed any drinking water contamination in the affected schools to the antiquated plumbing in the buildings.

Detroit’s drinking water comes from the Detroit River.

Water safety is a sensitive issue in Michigan, where lead contamination in the water supply of Flint prompted dozens of lawsuits and criminal charges against former government officials.

Medical research has linked lead to a stunting of children’s neural development. Exposure to copper can cause gastrointestinal distress and liver or kidney damage, according to the U.S. Environmental Protection Agency.

Flint switched its water supply to the Flint River from Lake Huron in April 2014 to cut costs. The corrosive river water caused lead to leach from pipes. Flint switched back to Lake Huron water in October 2015, but the contamination continued.