There are an innumerable number of things we take for granted in the United States. One would be that when you flip the switch the lights come on. The cell phone works. And water comes out of the faucet when you open it. Not only that, you depend on the food you buy and the medicines you take to be free from contamination. Your life depends on this.
Most of us assume that the water that comes out of the tap is safe to drink. Some areas of the world don't have safe water at all, and they know it. What if the water coming out of our taps isn't safe to drink, yet we assume it is? It could be argued that we're in worse shape than those who know their water is dangerous.
Evidence that drinking the water in US is presents dangers is on page two.