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Industrial companies are allowed to discharge chemicals into a river, a creek, or a stream with a permit.

Then the water goes to a water filtration and treatment plant.

The main purpose of drinking water treatment plants is to kill the bacteria that cause cholera and to remove particulates that make the water look impure.  Chemicals are added to the water to accomplish this. Water treatment plants are not capable of identifying, much less removing, the over 80,000 chemicals made, used and dumped in the water in the US every day. They pass right through. So do the pharmaceuticals that enter the water.