Stop me if you've heard this one before.

The people in charge of the drinking water in Flint didn't do their jobs correctly.

A state-appointed emergency manager forced the city to switch where they got their drinking water from to try to save money. The city switched water sources from Lake Huron water from Detroit, to water from the Flint River. And when they made the switch, they failed to understand that there was something Detroit was adding to the water to protect them.

Phosphates.

These phosphates create a protective layer inside drinking water pipes.

When they switched to the Flint River, these phosphates were no longer being added. The people in charge of the drinking water in Flint didn't understand the consequences.

When a guy from the EPA found out what was going on, he was alarmed. His name is Miguel Del Toral, and he's one of the country's foremost experts on how cities control for corrosion in their drinking water supplies.

Del Toral has examples of what happens to lead pipes when no corrosion control is used.

Mark Durno, the on-scene coordinator for the EPA in Flint, showed us these drinking water pipe samples.

Here's what they look like:

Listen to Durno explain what we're looking at below (*note, he identifies the corroded pipe as lead. It is not lead. It is galvanized, but the rusted flakes become a source for lead contamination):

Durno says the rusted flakes inside the corroded pipes become a source of lead contamination.

"When the scale flakes off... we do tend to see high levels of specifically lead and copper, depending on what type of pipe the water is flowing through," says Durno.

He explained the process further in an e-mail to us:

When lead pipes scale, the particles will accumulate where other pipes are corroding. When the large pieces break off of the heavily corroded galvanized pipes that are down-line from the lead service lines, they will contain lead and other metals (including zinc and copper). In essence, the heavy corrosion, as shown in the photo, becomes a lead contamination source. The corrosion that occurs in lead pipes is not as visible as it is in the galvanized pipe, but it still occurs when corrosion protection is not in place.

Michael Torrice of Chemical and Engineering News explains the chemistry at work here.

Torrice writes that the corrosion happens when "oxidants, such as dissolved oxygen or chlorine disinfectant, react with elemental iron, lead, or copper in the pipes."

More here:

“The distribution system acts like a geochemical reactor,” says Haizhou Liu, an environmental engineer at the University of California, Riverside. “There are miles and miles of pipes—some iron, copper, and lead—that get corroded.” … utilities treat their water to maintain a mineral crust on the inside surfaces of their pipes. This so-called passivation layer protects the pipes’ metal from oxidants in the water. The coatings consist, in part, of insoluble oxidized metal compounds produced as the pipe slowly corrodes. If the water’s chemistry isn’t optimized, then the passivation layer may start to dissolve, or mineral particles may begin to flake off of the pipe’s crust. This exposes bare metal, allowing the iron, lead, or copper to oxidize and leach into the water.

Some experts have said that the phosphates running through Flint's water distribution system will help resolve the problem.

But Mayor Karen Weaver said that kind of thinking is a "tough sell" for us. She says they'll never trust that something like that will work. She wants all the lead pipes in the city replaced in one year.

*Correction 2-13-2016 - an earlier version of this story identified all the pipes in the photo as "lead pipes." They are not all lead. The corroded pipe on the left is galvanized. We corrected the copy and headline above. We regret the error.