Four years ago, the city of Toledo told more than 450,000 residents to immediately stop drinking water out of the tap.
That's after a toxin called microcystin was detected in the water. The toxin came from a bloom of cyanobacteria that had surrounded the city's water intake in Lake Erie.
The incident caused panic among some residents, hoarding of water, even fights at bottled water distribution sites - along with a lot of unwanted national media attention.
And it taught the city some hard lessons.
What happens to the water Toledo takes from Lake Erie
Municipal water treatment is a painstaking and complicated process.