(CNN) Comedian Michelle Wolf made a lot of jokes at the White House Correspondent's Dinner that offended people.

But buried in the controversy was the line that ended her routine: "Flint still doesn't have clean water."

Indeed, it's been nearly four years since the Flint, Michigan, water crisis began, and although government officials claim the city's tap water is back to safe levels, residents still do not trust that the problem has been fixed for good.

For all the debate around the appropriateness of Wolf's barbs Saturday night, her blunt closing line underscored the seriousness of the long-running humanitarian crisis in Flint, where cost-cutting measures led to drinking water tainted by lead and other toxins.

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The problem began in 2014, when the city switched its drinking water from Lake Huron to the corrosive Flint River. Residents said the water looked, smelled and tasted funny, and gave people rashes and caused other health problems.