Flint is a like other northern American cities it's size (about 100,000). So its water quality problems could happen elsewhere in America. Flint uses a lot of salt in the winter to keep its roads passable during snow and frigid temperatures, about an incredible 135 pounds per person. All that road salt has to go somewhere; it is flushed by rain and runoff into the rivers and lakes--in this case the Flint River. What it does there is increase the waters' acidity and therefore its corrosive effect on things like lead pipes. Flint River water the corrosive index rose from 0.54 to 2.3 after the city switched its water supply from Detroit to the river to save money.
What local and state officials did not do was to comply with federal water quality rules, specifically the Lead and Copper rule passed in 1998 by installing a corrosion control system when they switched water sources. They did use more chlorine to purify the river water, so together with salt runoff contributions, chloride concentrations soared from 11.4mg/l to 92mg/l. Unfortunately that condition played havoc with the city's aging lead pipe distribution system. Twenty-seven thousand children in the city have been exposed to toxic levels (more than 200-1300 times the WHO standards) of lead contamination. Lead poisoning is particularly damaging to children's developing brain and nervous system. Despite the clear threat to public health, the MDEQ downplayed the problem, saying the water quality controversy was "near-hysteria". At one point a state official even lied to investigating EPA official, saying that Flint "has...an optimized corrosion control program". Propaganda is usually cheaper than action.