A spokesman for the governor said Thursday that he had not been briefed by his aides on the issue until January, shortly before he made his public statements on it.

“He took action promptly and released the information publicly,” the spokesman, Dave Murray, said.

Concerns about Flint’s water have largely focused on the presence of lead. Since Flint, a shrinking city of fewer than 100,000, switched its source in April 2014 to save money, the water has had rising, dangerous lead levels as well as unsafe levels of fecal coliform bacteria. After extra chlorine was added to treat that bacteria, levels of a contaminant from extra chlorine also increased.

But at the same time, the emails suggest, county health officials were noting another problem: a wave of Legionnaires’ disease cases.

In Genesee County, which includes Flint, state officials say there have been 87 cases of Legionnaires’ disease since June 2014, and nine associated deaths. But state officials and some experts say they are unsure whether the rise in cases is tied to the city’s water. People contract the disease by breathing in mist or vapor that has Legionella bacteria, which is often found in warm water. According to federal estimates, American hospitals treat 8,000 to 18,000 people with the disease each year.

“We cannot conclude that the increase is related to the water switch in Flint, nor can we rule out a possible association,” Angela Minicuci, a spokeswoman for the Michigan Department of Health and Human Services, said Thursday. About 35 percent of the people who became sick received City of Flint water in their homes, Ms. Minicuci said, but about 30 percent did not, and had no known exposure to the city’s water system in the two weeks before they became ill.