National Geographic: Rains that have flooded portions of the middle part of the United States have damaged buildings, swept away cars and houses, and killed at least 18 people in Texas and Oklahoma. And with a chance of more rain forecast this week, these hard-hit areas aren't out of the woods yet.
In Texas, the enormous amount of stormwater has overwhelmed some treatment facilities, washing chemicals and toxic substances into the mix, including raw sewage, crude oil, and pesticides.
"Anything you would find on...