You've probably lived somewhere with leaded pipes. They are very common. Across the country we are working to replace leaded pipes when we can, but the problem is very complex. As it turns out, it's much more cost-effective to treat water than embark upon giant infrastructure projects. Simply put, the MDEQ, and the EPA should have known to treat the water, which would have kept the lead from leeching into the water. Unfortunately, this wasn't done, and now the pipes are damaged - perhaps beyond repair.
Despite the above, the water problems in Flint can't be attributed to a single thing, but rather a culmination of failures in state and local government best described as a problem of culture. Instead of a culture of openness and communication, there are indications the state, and to a lesser degree, the local government embraced a culture of only communicating good news and spinning or squashing bad news - even internally.
Even kwami kilpatrick, the ex-mayor of detroit who is now in prison, said he knew about the water problems when he was in office.