> This precipitated the tragic decision in 2013 to end the city’s five-decade practice of piping treated water for its residents from Detroit in favor of a cheaper alternative: temporarily pumping water from the Flint River until a new water pipeline from Lake Huron was built. Although the river water was highly corrosive, Flint officials failed to treat it, and lead leached out from aging pipes into thousands of homes.

https://en.wikipedia.org/wiki/Flint_water_crisis#Lead_exposu...

> The documents falsely claim that the city had tested tap water from homes with lead service lines, and therefore the highest lead-poisoning risks; however, the city did not know the locations of lead service lines, which city officials acknowledged in November 2015 after the Flint Journal/MLive published an article revealing the practice, using documents obtained under the Michigan Freedom of Information Act. The Journal/MLive reported that the city had "disregarded federal rules requiring it to seek out homes with lead plumbing for testing, potentially leading the city and state to underestimate for months the extent of toxic lead leaching into Flint's tap water."

Then Flint decided to save money by changing water sources from Lake Huron to the Flint river which changed many properties of the water including ph. This relatively abrupt change caused the biofilm and mineral coating to weaken and expose the lead of the pipes to the water.

So are lead pipes at fault or the sudden change in water chemistry? Water chemistry changes are well know to cause these issues, the water quality chemist in most jurisdictions will be aware of the potential issues, not sure if they were ignored.

IMO the pipes should have been changed out long ago, but that doesn't absolve the decision makers from the issues caused by changing water sources to save money without consideration for the side effects.