The statement also said lead had not been found in the Newark Water Department’s source water, meaning the broader public was not at risk.

“In the vast majority of cases where lead is found in drinking water, it enters through the water delivery system itself when it leaches from either lead pipes, household fixtures containing lead, or lead solder,” said the statement, which was released by the state environmental department, which performs the testing.

But Ms. Gentleman-Cheatham had been so unsettled by the news that she told her children not to drink the tap water at the family’s house in Newark. She was afraid it was all contaminated. She said she had chosen to buy bottled water, an unexpected cost that ate into her family budget.

An annual report on lead poisoning issued in 2014 by the state’s Health Department found that Newark led every other large municipality in the number of children under the age of 6 with elevated levels of lead in their blood, as well as the greatest increase in lead poisoning reported from 2013 to 2014.

Even before the water was turned off in the 30 city schools, state lawmakers held hearings about the dangers facing children in the state because of exposure to the contaminant in their homes, where lead-based paint may still remain.

“You can spend money now, or you can spend later,” Staci Berger, president and chief executive officer for the Housing and Community Development Network of New Jersey, told lawmakers according to the online publication New Jersey Spotlight. “We can absolutely fix this if we put the resources into it.”

Dr. Irwin Redlener, president of the Children’s Health Fund and a professor at the Mailman School of Public Health at Columbia University, said that lead in drinking water was a problem with immediate health consequences, especially for children, but that the recent revelations about contamination offered another ominous warning about the general state of the country’s infrastructure.