I assume the chemical will be added at offending points in the system, such as a pumping station, long before it hits the treatment plant. If the author gives the impression it will be added right before final discharge to the environment, I think that is probably incorrect.
Yes I think he is incorrect on the point you made (before discharge) and incorrect when he said it was going to be added to drinking water. Like I said, I get the impression he is clueless. Have a great day.