The primary cause of the Flint water crisis was lead contamination in the water supply. The water source was switched to the Flint River in 2014, which led to corrosive water corroding the city's aging pipes and causing lead to leach into the water. This resulted in elevated levels of lead in the drinking water, which is a serious health hazard. The lead contamination was linked to various health problems, especially in children. The other options you mentioned, total trihalomethanes, Legionella pneumophila, and Escherichia coli, were not directly related to the Flint water crisis.
