Legionnaire’s Disease is a potentially fatal pneumonia caused by inhaling Legionella bacteria.  These bacteria can live in the organic matter lining drinking water pipes.  Corrosive water dissolves the protective mineral lining in pipes and then leaches iron out of old iron pipes. Iron is a micronutrient that boosts Legionella reproduction. The metal also reacts with and inactivates chlorine disinfectant that otherwise would kill the bacteria.

Water in homes supplied with Flint River water had  Legionella concentrations roughly seven times as high as those found in the baseline surveys. High levels of iron were found in the Flint homes and hospitals using Flint River water, but no iron was found in nearby businesses using Detroit water. In more than half the water samples from homes supplied with the treated Flint River water, the researchers could not detect any chlorine. No Legionella bacteria were detected in the buildings using Detroit water.