The cleanliness of the Flint River and the lead in people’s pipes are two different problems.
The problem in the Flint River as many other rivers all over in rural areas is from runoff from the fields. Agricultural areas are and have always been built around natural waterways. So the runoff makes the river dirty; but lots of rivers are dirty and people dont drink leaded water.
Places all over still have lead pipes underground leading to your house from the road. Water even comes into your house in lead and at the meter it switches to something else like copper or galvanized.
People whose houses are on city water service are at the mercy of the water department to keep them safe and lead-free.
What caused this situation in flint is they had an “emergency financial manager” who cut out the treatment regimen that stops the river water from sucking lead out of the pipes in peoples homes or on the way to peoples homes. These people had no idea and they kept on using the water for everything from watering their plants to eating and drinking. Then they (the government) tried to cover it up. When everybody found out the water was leaching this lead from the pipes it was too late. Now everybodys pipes (houses) who never had a problem are all contaminated with lead throughout and the pipes have to be removed and replaced. And the pipes in the ground which are lead or contaminated by lead; those have to be replaced too.
The bigger problem with flint is its not just flint. Its every city with old water pipes with old houses with people living in them are at risk of this happening to them. All the families and hipsters moving into old neighborhoods and gentrifying them and fixing up their houses to the T’s usually dont replace the city water service to the house because its cost prohibitive. They want to spend 20k on something they can look at, not something that COULD be a problem.