The latest contaminated water problem in the US is in Flint Mi. LINK
from contaminated river water
but a couple years ago, it was in Washington DC
the lead pipe problem
Lead is a major cause of ADHD and mental retardation and we used to screen our 2 year olds for it.
In the past, it was from kids eating flaked paint in older buildings, before they stopped using it in paint. (lead is sweet) and some from leaded gas air pollution.
The Flint problem will be politicized, but it is actually the tip of an iceburg: When I lived in Appalachea, our drinking water was upstream from the mine runoff, but everyone went to springs for water or bought it in the grocery store.