Millions of people are exposed to unsafe drinking water every year in the US.

Industrial towns like Pittsburgh and Detroit have discovered unsafe levels of lead in their water, which can lead to permanent brain damage in children.

Other cities are reeling from the aftermath of chemical spills, which have released toxic substances into their main water supplies.

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Imagine turning on the tap in the morning to find an unpleasant brown sludge that tastes like metal. Then imagine that state officials told you that water was safe to drink.

That was the reality for residents of Flint, Michigan in 2014, when lead from aging pipes seeped into their water system, effectively poisoning an entire community.

Read more: Erin Brockovich is warning about an emerging drinking-water crisis in the US. Here's how she recommends you protect yourself.

The scandal was one of the most egregious instances of water contamination in the US, but it wasn't an isolated occurrence. Every year from 1982 to 2015, between 9 million and 45 million Americans got their drinking water from a source that violated the standards of the Environmental Protection Agency (EPA).

While rural areas are the most contaminated, a few major cities have struggled to renovate their aging pipes and enforce safe standards among local jurisdictions. Here are some of the cities with the worst tap water in the US.