A prominent water quality story in the news in recent months has been the high levels of lead found in Flint, Michigan drinking water. About 25% of Flint households have lead levels above the federal standard of 15 parts per billion (ppb), with one home having an almost unbelievable level of 13,200 ppb. It’s a sordid story, with shocking inaction and apparent malfeasance by authorities. But why are there are such high levels of lead in Flint’s water? The problem came about after Flint switched their drinking water source from Detroit, i.e., Lake Huron, to the Flint River in 2013. The high levels of lead are not in the Flint River, but rather the water is corroding old iron pipes that are part of Flint’s water infrastructure. Why is that?

The Flint River has much higher levels of chloride (Cl^-) than Lake Huron. Chloride is a very corrosive ion to metals, including iron and lead. Flint also apparently doesn’t add a corrosion inhibitor chemical to reduce corrosion, like Detroit does. Another problem caused by iron corrosion is that the reaction consumes chlorine, which is added to prevent the growth of microorganisms. Thus it’s very difficult to maintain an appropriate chlorine residual to prevent the growth of microorganisms.

The source of chloride in the Flint River is undoubtedly due to road salt runoff. This is a water quality problem found in my water bodies in the northern U.S., Canada, and Europe, which I have blogged about before [see here, here, and here].