In front is an ACTUAL water pipe from Flint. In the back are what they should look like.

[Nye Bevan]

11. That's "tuberculation" which is not considered to be a health hazard.

Jagged mounds of metal protruded from all sides of the pipe’s interior. Liver red and gooey brown, with purple highlights and dirty yellow streaks. It made me think of those angiogram images of the sclerotic arteries of people on the verge of a fatal heart attack.

This is “tuberculation,” the formation of corrosion on the inside of cast-iron pipes that’s been a known hazard in old water systems since the 1950s, when scientists at the University of Illinois exploded the myth that cast iron doesn’t easily corrode.

It does. Tuberculation comes from the interaction between iron and the “chemistry” of our water, Art Shapiro, Baltimore’s water engineer, tells me. Among the factors are the pH and alkalinity of the liquid flowing through the pipes, along with calcium and the chlorine injected to make it safe.

Thus, did our award-winning water slalom and zigzag around these foul-looking blisters in our 2-inch main – picking up particles of brown sediment that now covered my hands – until something cracked (that manifold, I guess), and the city was forced to replace this rotted remnant of an out-of-date network with a couple feet of clean pipe.

Health officials consider rust and iron in water not to be a health hazard. According to Shapiro, you get more iron from a supplement pill than from the sediment that courses through the city’s pipes.

https://www.baltimorebrew.com/2013/10/25/my-close-encounter-with-a-baltimore-water-pipe/

I hope you don't seriously think that all the city water pipes in Flint looked like the one at the back prior to April 2014 when the supply was switched to the Flint River.