Officials said unfiltered water was still not safe to drink, and the long-term effects of drinking the tainted water for more than a year remain a worry, particularly for parents of small children.

The only city worker charged so far in the Flint crisis is Michael Glasgow, the city’s laboratory and water quality supervisor, who is accused of tampering with evidence — lead testing reports — and willfully neglecting his duty.

The arrest of Mr. Glasgow, 40, came as a surprise to some, largely because he had cooperated with authorities, and had personally sought water samples last year from a home that was reporting high levels of lead. Mr. Glasgow also had voiced early concerns about switching the city’s drinking water away from Detroit’s water system to a new source in 2014, the event that set off the crisis that left residents drinking odd-smelling, foul-looking, lead-tainted water for months.

Robert Harrison, a lawyer for Mr. Glasgow, said he could not comment on the specific charges, but described his client as “an honest, decent person” who had spent years working for the city of Flint and had worked his way up from the bottom.

“Criminal charges against Mike are difficult to understand, given what Mike did in this case,” Mr. Harrison said. “Not only was Mike strongly and publicly opposed to the transfer of the water system away from the Detroit system, but Mike voluntarily met with, and spoke with, numerous investigators from the attorney general’s office and the Genesee prosecutor’s office on several occasions.”

In an email Mr. Glasgow sent to state regulators a little more than a week before Flint was to switch from its water supply to a new source, the Flint River, he expressed doubts about the monitoring of water safety and the training of workers at the Flint water plant.