It's really a combination. They changed their water source, which changed their chemistry, which changed the propensity to leach lead into the water. If they had done that and not had the lead pipes, obviously there would not have been a problem, but because they had that change and they did have the lead pipes, that sleeping menace that people had forgotten about suddenly contaminated the water in some homes to astronomical levels.
It's really a combination of effects. Obviously, if they didn't have the lead pipes, they would not have had the problem.